Commercial terahertz spectrometers operating at frequencies from 0.1 to 3.0 THz are widely used in academic and industrial research labs. Most time-domain terahertz systems are based on terahertz generation via photoexcitation of photoconductive switches with femtosecond lasers and require highly efficient terahertz emitters in order to achieve good system performance. However, for many terahertz sources, long-term stability and high conversion efficiency is still lacking.

Two new concepts for terahertz generation overcome these problems. The first is a biased large-area photoconductive emitter with high conversion efficiency and the second concept is a new approach to the generation of intense terahertz radiation based on the photo-Dember effect—a technique that does not require a bias voltage. The large-area design of both concepts enables scalability toward high terahertz electric fields, enabling both high signal-to-noise ratios and short acquisition times.

Multiplexed terahertz emitters can be based on the principle of a photoconductive switch (a) or lateral photo-Dember currents (b).

Continue reading the full article by THOMAS DEKORSY, JURE DEMSAR, STEPHAN WINNERL, MATTHIAS BECK, and GREGOR KLATT at OptoIQ.com.

A team in the Advanced Diagnostics & Therapeutics (AD&T) Initiative at the University of Notre Dame has been awarded a grant of $359,281 for the development of a room-temperature, portable terahertz (THz) imaging system from the National Science Foundation (NSF) via the Integrative, Hybrid and Complex Systems (IHCS) program.

Led by Research Assistant Professor Lei Liu, Associate Professor Grace Xing and Professor Patrick Fay of the Department of Electrical Engineering, the team is working to develop an imaging device and nano-scale detectors that would create such a system, one that would more affordably capture high-quality images in real time at room temperature.

According to Liu, who will design the overall system and test the THz detectors developed by the team, the entire system would operate like a camera but in the submillimeter-wave and THz range of the electromagnetic spectrum — between radio frequency and the optical region.

“The development of such a system is important, not only because it does not require extensive cooling equipment but also because of the potential applications it enables across a variety of fields,” he said.

THz waves (and subsequent imaging systems) are ideal for medical applications because they are non-ionizing, meaning they do not damage living tissue in the same way that X-rays can. They are able to provide high-resolution images because of their short wavelengths, and this wavelength range also provides the ability to detect differences in tissue density more effectively than X-rays. For example, even though breast magnetic resonance imaging machinery does not use ionizing radiation, the units themselves are bulky and do not always provide accurate images. The system that the Notre Dame researchers are developing shows promise in enhanced cancer diagnostics, the early identification of disease biomarkers and increased quality of pharmaceuticals, detecting impurities or defects.

In addition, submillimeter-wave and THz waves can penetrate fabrics, plastics and cardboard, so they can easily be used in security applications to reveal concealed weapons or devices. In military applications, they could also prove useful by more effectively targeting specific ranges of materials or objects, as well as being able to accurately sense traces of explosive elements.

The goal of the IHCS program is to design, develop and implement novel complex and hybrid systems that lead to innovative engineering solutions for a variety of fields including, but not limited to, healthcare, medicine, the environment, communications, disaster mitigation, homeland security, transportation, manufacturing, energy and smart structures.

Established in 2008, AD&T is an interdisciplinary research initiative focused on developing diagnostic and therapeutic technologies at the smallest molecular scales to address a diverse set of health and environmental challenges.

For more information about research initiatives within the AD&T, visit http://advanceddiagnostics.nd.edu.

Source: South Bend Tribune.

It’s a sign of the times when the speed of electrons moving through wires is seen as pedestrian, but that’s increasingly the case as technology moves towards the new world of optical communication and computing. Optical communication systems that use the speed of light as the signal are still controlled and limited by electrical signaling at the end. But physicists have now discovered a way to use a gallium arsenide nanodevice as a signal processor at “terahertz” speeds that could help end the bottleneck.

The new discovery, made by researchers at Oregon State University (OSU), the University of Iowa and Philipps University in Germany, has identified a way in which nanoscale devices based on gallium arsenide can respond to strong terahertz pulses for an extremely short period, controlling the electrical signal in a semiconductor. The devices can be used as optical switches, replacing wires with emitters and detectors that can function at terahertz speeds.

Yun-shik Lee, an associate professor in the OSU Department of Physics, says the first applications of this type of technology would probably be in optical communications of almost any type – video, audio or others. However, the ultimate application could be quantum computing, in which computers would be orders of magnitude faster than they are now, working with a different physical and logic basis, not even using conventional transistors. Among other uses, Lee says their extraordinary speeds would make them extremely valuable for secure codes and communications.

“This could be very important,” Lee said. “We were able to manipulate and observe the quantum system, basically create a strong response and the first building block of optical signal processing.”

The team’s research appears in the journal, Solid State Electronics.

Source: GizMag.

Infrared (IR) and terahertz (THz) light is extremely sensitive to different material properties and thus can be used for characterizing chemical composition, crystal structures as well as conduction properties. However, due to the diffraction-limited spatial resolution, conventional techniques cannot be applied to image local material properties in nanostructures or nanodevices This problem can be tackled by near-field optical microscopy that uses a sharp tip to focus the light to nanoscale spot sizes, thus allowing to generate two-dimensional (2D) maps of surfaces with a spatial resolution far below the diffraction limit. “By developing novel near-field techniques paired with computed image reconstruction, we now want to develop three-dimensional (3D) near-field microscopy. This shall allow to image the inside of nanostructures with IR and THz light, in a similar way as Computed Tomography (CT) sees inside the human body” says Rainer Hillenbrand.

Rainer Hillenbrand earned his PhD from the Technische Universität München for research and development in optical near-field microscopy. From 2003 to 2008 he was Head of the Independent Junior Research Group “Nano-Photonics” at the Max Planck Institute of Biochemistry, which was funded within a Nanofutur grant awarded by the German Federal Government for Education and Research. As anticipated by the Nanofutur project, in 2007 the spin-off company Neaspec GmbH was founded with the mission to develop IR and THz near-field microscopes for the research laboratory and to promote their industrial applications. Since 2008 Rainer Hillenbrand continues his scientific research activities as an Ikerbasque Research Professor (Basque Foundation for Science) and Nanooptics group leader at CIC nanoGUNE in San Sebastian, Spain.

Rainer Hillenbrand is already the forth winner of an ERC grant within CeNS in 2010: The other grantees are Philipp Tinnefeld, Dieter Braun and Thomas Klar. Furthermore, two other CeNS members were awarded with this prestigious grant already in 2009: Jens Michaelis (LMU Munich) and Matthias Schneider (at that time at the University of Augsburg).

ERC Starting Independent Researcher Grants (ERC Starting Grants) aim to support up-and-coming research leaders to establish or consolidate their independent research group. Being a very competitive program, proposals are assessed only in terms of their scientific excellence, and less than 10% of the applications were accepted in the 2009 call.

Source: NanoWerk News

The new, all-optical system, using terahertz (THz) wave technology, has great potential for homeland security and military uses because it can “see through” clothing and packaging materials and can identify immediately the unique THz “fingerprints” of any hidden materials.

Terahertz waves occupy a large segment of the electromagnetic spectrum between the infrared and microwave bands which can provide imaging and sensing technologies not available through conventional technologies such as x-ray and microwave.

“The potential of THz wave remote sensing has been recognized for years, but practical application has been blocked by the fact that ambient moisture interferes with wave transmission,” says Xi-Cheng Zhang, Ph.D., director of the Center for THz Research at Rensselaer.

Dr. Zhang, the J. Erik Jonsson Professor of Science at Rensselaer, is lead author of a paper to be published next week in the journal Nature Photonics. Titled “Broadband terahertz wave remote sensing using coherent manipulation of fluorescence from asymmetrically ionized gases,” the paper describes the new system in detail.

The “all optical” technique for remote THz sensing uses laser induced fluorescence, essentially focusing two laser beams together into the air to remotely create a plasma that interacts with a generated THz wave. The plasma fluorescence carries information from a target material to a detector where it is instantly compared with material spectrum in the THz “library,” making possible immediate identification of a target material.

“We have shown that you can focus a 800 nm laser beam and a 400 nm laser beam together into the air to remotely create a plasma interacting with the THz wave, and use the plasma fluorescence to convey the information of the THz wave back to the local detector,” explains Dr. Zhang.

Repeated terrorist threats and the thwarted Christmas Eve bombing attempt aboard a Delta airline heightened interest in developing THz remote sensing capabilities, especially from Homeland Security and the Defense Department, which have funded much of the Rensselaer research.

Because THz radiation transmits through almost anything that is not metal or liquid, the waves can “see” through most materials that might be used to conceal explosives or other dangerous materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks and book bags.

Unlike x-rays, THz radiation poses little or no health threat. However, the technique cannot detect materials that might be concealed in body cavities.

“Our technology would not work for owners of an African diamond mine who are interested in the system to stop workers from smuggling out diamonds by swallowing them,” Dr. Zhang says.

Though most of the research has been conducted in a laboratory setting, the technology is portable and eventually could be used to check out backpacks or luggage abandoned in an airport for explosives, other dangerous materials or for illegal drugs. On battlefields, it could detect where explosives are hidden.

The fact that each substance has its own unique THz “fingerprint” will show exactly what compound or compounds are being hidden, a capability that is expected to have multiple important and unexpected uses. In the event of a chemical spill, for instance, remote sensing could identify the composition of the toxic mix. Since sensing is remote, no individuals will be needlessly endangered.

“I think I can predict that, within a few years, the THz science and technology will become more available and ready for industrial and defense-related use,” predicts Dr. Zhang.

Source: PhysOrg.com.

TeraView currently offers a range of the most advanced, cutting edge THz spectrometers in the world. One of TeraView’s leading products, the CW Spectra 400(TM) utilizes the sub-licensed technology. The system generates a continuous wave which has a tunable frequency that is emitted and detected via a set of proprietary, fibre-fed THz photomixers. By the addition of suitable supports, gantries or other units, the CW Spectra 400(TM) is capable of performing spectroscopy and imaging on a range of objects and materials. Under the terms of the Sub-Licensing Agreement, T-Ray Science will collect royalties on the sales of this product and any other products that utilize CW generation in the United States.

According to BCC Research, overall spectroscopy sales in the US are expected to reach $5.2 billion this year, with an average annual growth rate of 7.7%. Furthermore, BCC Research estimates the THz imaging market will be worth $207 million by 2018, with a compound annual growth rate of 37.2% for the period between 2013 and 2018.

“THz technology is different from other methods because one can image things as well as take measurements,” said Thomas Braun, President of T-Ray Science. “We believe that a significant percentage of the THz market will go to CW THz devices due to their relative affordability versus other types of THz instruments. Therefore, CW THz technology is very well positioned to compete in a market that demands mass production, low cost, and portability.”

T-Ray’s Science’s platform THz imaging technology has been shown to have numerous potential applications including homeland security, the detection of explosives and ceramic knives, process control in the paper, plastics, petro chemical and pharmaceutical industries, and medical imaging for detection of skin and other cancers. THz waves are also a safe, accurate, and economical alternative to other scanning methods such as high frequency ultrasound, magnetic resonance imaging, and near-infrared imaging. This emergent technology has the potential to revolutionize the way many diseases are diagnosed, and ultimately cured. Numerous studies have shown that THz imaging can be used to image various cancers of which skin cancer imaging continues to be the focus of T-Ray Science’s research and development.

More About TeraView Ltd.
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By combining a detector and laser on the same chip to make a compact receiver, the researchers rendered unnecessary the precision alignment of optical components formerly needed to couple the laser to the detector.

The new solid-state system puts to use the so-called “neglected middle child” frequency range between the microwave and infrared parts of the electromagnetic spectrum.

Terahertz radiation is of interest because some frequencies can be used to “see through” certain materials. Potentially they could be used in dental or skin cancer imaging to distinguish different tissue types. They also permit improved nondestructive testing of materials during production monitoring. Other frequencies could be used to penetrate clothing, and possibly identify chemical or biological weapons and narcotics.

Since the demonstration of semiconductor THz quantum cascade lasers (QCLs) in 2002, it has been apparent that these devices could offer unprecedented advantages in technologies used for security, communications, radar, chemical spectroscopy, radioastronomy and medical diagnostics.

Until now, however, sensitive coherent transceiver (transmitter/receiver) systems were assembled from a collection of discrete and often very large components. Similar to moving from discrete transistor to integrated chips in the microwave world and moving from optical breadboards to photonic integrated circuits in the visible/infrared world, this work represents the first steps toward reduction in size and enhanced functionality in the THz frequency spectrum.

The work, described in the current issue (June 27, 2010) of “Nature Photonics,” represents the first successful monolithic integration of a THz quantum-cascade laser and diode mixer to form a simple, but generically useful, terahertz photonic integrated circuit — a microelectronic terahertz transceiver.

With investment from Sandia’s Laboratory-Directed Research and Development (LDRD) program, the lab focused on the integration of THz QCLs with sensitive, high-speed THz Schottky diode detectors, resulting in a compact, reliable solid-state platform. The transceiver embeds a small Schottky diode into the ridge waveguide cavity of a QCL, so that local-oscillator power is directly supplied to the cathode of the diode from the QCL internal fields, with no optical coupling path.

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The Sandia semiconductor THz development team, headed by Michael Wanke, also included Erik Young, Christopher Nordquist, Michael Cich, Charles Fuller, John Reno, Mark Lee — all of Sandia labs — and Albert Grine of LMATA Government Services, LLC, in Albuquerque. Young recently joined Philips Lumileds Lighting Co., in San Jose, Calif.

The paper is available online at: http://dx.doi.org/10.1038/NPHOTON.2010.137 . Abstracts are available to everyone; full text only to subscribers.

The GaN detector forms a so-called plasma wave of the electrons, in which the electron density is fluctuated as a wave. The plasma wave resonates with the incident THz wave, which is detected as an electric signal at the GaN transistor. The use of GaN with high electron velocity effectively increases the amplitude of the plasma wave and the extracted electric signal. The detector uses the gate electrode itself as a dipole antenna free from the loss in the transmission lines. In addition, the source and the drain electrodes of the GaN transistor are designed to work as parasitic elements for the antenna, which effectively confine the incident THz wave in the vicinity of the gate. Note that the employed metal-oxide-semiconductor (MOS) gate structure reduces the gate leakage current suppressing the leakage of the plasma wave around the gate antenna. The choice of the material together with a novel antenna structure successfully increases the sensitivity of the THz detector.

The fabricated THz detector using Panasonic’s proprietary GaN technologies achieves a very high sensitivity of 1100 V/W at room temperature, while a conventional detector utilizing thermal conversion requires cooling of the device down to -270°C to maintain high enough sensitivity. The developed GaN-based THz detector free from such cooling systems can make the THz systems very compact keeping high sensitivity.

Applications for 9 domestic and 1 overseas patents have been filed. These research and development results have been presented at 68th Device Research Conference, held in South Bend, Indiana, U.S. from June 21 to 23, 2010.

Source: Panasonic.

“At lower frequencies, in the Terahertz range, which is situated between the frequencies of the infrared light and microwave radiation in the electromagnetic spectrum, far more complex motions take place involving motions of whole water molecules relative to each other”, explains Terahertz specialist Prof. Havenith-Newen. “In particular, these motions involve closing and breaking of the three dimensional hydrogen bond network of water, which interconnects water molecules and is responsible for the unique properties of water.”

Observations of this kind have become feasible only lately with the development of advanced laser light sources.

Studies performed at the RUB lead to the discovery of an unexpectedly long ranged influence of biologically relevant solutes, such as sugars and proteins, on the motions of water, the so-called “Terahertz-dance” of water (“Dissecting the THz spectrum of liquid water from first principles via correlations in time and space”). In the vicinity of the molecule, water motion is highly ordered: “While water molecules usually behave like disco dancers, in the proximity of biomolecules they perform a minuet”, says Prof. Havenith-Newen. However, until now a detailed explanation of this unexpected phenomenon was not available.

Dance of water molecules.

The choreography of water

The underlying vibrational motions between water molecules are extremely complex. So far it was not possible to explain the experimental result with a molecular mechanism. In a joint effort, scientists of both departments performed molecular dynamics simulations of water, which in contrast to conventional approaches, are not based on empirical models for the interactions between molecules, but employ ab initio calculations. For the first time such simulations have been carried out on a scale which allows for statistically meaningful statements about the comparably slow vibrational motions between the water molecules. These extensive calculations were supported by the Leibniz Computing Center in Garching near Munich, which granted access to computational resources on the national supercomputer HLRB2. The use of newly developed analysis methods yielded a precise description of the THz vibrations in water as a correlated motion of many water molecules: a sort of motion of water droplets within the water. “Therefore we have uncovered ‘the choreography of pure water’ at low frequencies”, says Prof. Marx.

Perturbed choreography

If another substance, such as a protein, is dissolved in water, it “perturbs” this choreography at its interface. This allows for a qualitative understanding of the experimental results using THz spectroscopy. “The correlated motions of water molecules at THz frequencies exhibit entirely new characteristics, which are significantly different from the well-known infrared vibrations of the chemical bonds within a molecule”, explains Prof. Marx. As this study shows, the latter are well described as localized vibrational motions within single molecules as well as direct neighbors. This is in stark contrast to the choreography of the THz dance of water: Here, many water molecules, connected only indirectly via hydrogen bonds, move together in a concerted motion in space and time. It is the change of this correlation, evoked by the biomolecule-water interface, which is detected by THz spectroscopy and used for technological applications.

Source: NanoWerk.com

It is a single cork, from Portugal, where 320 million pounds of bottle stoppers are produced every year. The billion-dollar cork industry is in trouble from a chemical that ruins the taste of wine. That is why physicist John Federici is bombarding the cork with terahertz rays, which can detect minute traces of the chemical.

But to Federici and other researchers at NJIT, these X-ray-like waves also may offer a first line of defense against suicide bombers and biological terrorists.

Bad corks, terrorism, natural disasters — it is all one to the scientists at NJIT, one of the top homeland security research universities in the country, where $100 million a year in anti-terrorism research translates into products with a vast range of applications.

John Federici, Distinguished Professor of Physics, poses with a Terahertz Interferometric Imaging Array in his lab at NJIT. The array uses terahertz rays to see through clothing and containers to detect concealed objects in real time. As the technology is improved Federici says it can be used in defense against suicide bombers and other terrorist activities.

Since 2004, when the Newark-based university was designated as the site of the New Jersey Homeland Security Technology Systems Center, researchers have applied an “all-hazards” approach to making life in the U.S. a little safer.

“High-tech, low-tech, we can’t afford to overlook any possibility in dealing with mass casualty events,” said center director Donald Sebastian. “You need multiple methods of detection and response. Terrorism comes in many forms; you have to see, smell, taste and analyze everything.”

NJIT has developed a multisystem approach that includes not only advanced detection but communications software that can warn the good guys when the bad guys are up to something.

There are the terahertz, or THz, rays that can leap from detecting bad corks to identifying people who are attempting to smuggle explosives or smallpox into a crowded room. And pattern recognition programs, equally capable of detecting someone lying to immigration officers, buying unusual amounts of suspicious chemicals or casing cars in a mall parking lot.

The research ranges from software for tracing the phone- and internet-usage patterns of home-grown terrorists — which recently helped police track down Faisal Shahzad, charged as the would-be Times Square bomber — to massive blimps designed to hover 12 miles above the Earth, sending back detailed scans of grids covering 500,000 square miles.

“Just because the most recent attacks like the Dec. 25 plane incident or the Times Square car bomber have been primitive and unsuccessful doesn’t mean there aren’t serious, sophisticated enemies probing our weaknesses every day,” said Rep. Bill Pascrell (D-8th Dist.), who last week introduced the bipartisan Weapons of Mass Destruction Prevention and Preparedness Act.

“Intelligence reports predict a significant threat of biological attack on the U.S. by 2013, and we must be prepared,” said Pascrell, a member of the House’s Homeland Security Committee. “The center at NJIT is key to developing a homeland security technology that will help us predict who will attack, what kind of attack, how we prepare, how we respond and how we recover.”

Pascrell helped funnel federal homeland security funding to NJIT. Added to military and National Science Foundation grants over the past five years, the funding placed the New Jersey Institute of Technology in the top 10 engineering universities in the nation, Sebastian said.

PRACTICAL USES
The role of the center is to take existing research and develop workable prototypes. For example, THz technology was isolated about 15 years ago, but applications were limited.
Terahertz waves operate in a similar manner to X-rays and microwaves but on a different bandwidth. Their beauty, said Federici, is that they can scan objects and people without any radiation threat, but are still capable of detecting hidden materials such as explosives and chemicals in amounts as small as parts per billion.

Each chemical emits a signature image that can be captured in real time. That means a person walking through an airport could be scanned without stopping and the imaging system could immediately detect minuscule amounts of anthrax or smallpox.

Federici’s team is developing a cost-effective system that uses a digital video camera to read the scanning results. It would be able to see through barriers such as packaging, corrugated cardboard, walls, clothing, shoes and pill coatings.

Silver foil blocks THz waves, Federici noted, but “it’s hard to walk through a detection system wearing silver foil underpants and not raise suspicion.”

On a purely practical level, life for airline passengers might become a little easier, Sebastian said, because “airport security would immediately know if the shampoo bottle contained benzene or the deodorant stick was really C-4. You could carry as much shampoo as you want because the scanner could identify the contents of the bottle without opening it.”

Scanners and pattern-recognition programs being developed at NJIT — ones that can detect anomalies not only in movement but in facial expressions — would have applications far beyond detecting jihadist plots, experts say.

Smart cameras could track evacuation during disasters such as hurricanes and alert police to potential looters. Smart guns would refuse to fire for anyone but the owner. Computerized noses could sniff and find deadly chemicals.

“I am fascinated by the work at NJIT because it can be applied cross-disaster,” said Charles McKenna, head of the New Jersey Office of Homeland Security and Preparedness. “We are particularly interested in computer profiling, which is much more sophisticated, and quicker, than traditional racial profiling.

“Jihad, Crips, extreme animal-rights activists, it’s all the same: people trying damage the system,” added McKenna. “We need every trick in the book to avert disaster.”

The best prevention systems on the planet, however, aren’t worth much if the word doesn’t get out, Sebastian said.

“None of this works without an integrated communications system connecting local, state and federal agencies — and that we still don’t have in this state or this country,” he said.

“It’s been nine years since 9/11 and we haven’t accomplished that because we are trying to patch rather than replace an inadequate communications system,” Sebastian added. “It’s time to get with the program.”

Source: NJ.com

“Spectrum Detector’s products are so remarkably complementary to ours that the decision to acquire the company was simple to make, and both sides are very excited to work together”, says Mr. Michel Giroux, president and CEO of Gentec Electro-Optics. Spectrum Detector products cover areas left ignored by the other laser measurement players, and that has been the company’s business model from the beginning. “Classic laser measurement products were already out there, so when we founded Spectrum Detector, we decided to aim wider, and pursue applications that were ignored by others”, mentions Mr. Don Dooley, president and founder of Spectrum Detector. With this idea in mind, and within just a few years, Spectrum Detector managed to develop an extensive line of sensors and instruments for laser and terahertz measurement, and have provided NIST with many custom instruments used as optical calibration transfer standards.

With the addition of Spectrum Detector products, Gentec Electro-Optics will now have measurement solutions for the new and rapidly expanding THz market, ultra-sensitive optical Joulemeters for applications down to femtojoules, instruments for pulse to pulse energy measurements up to 130 kHz and Optical TRAP detectors that act as primary calibration standards, to name a few.

With the acquisition, a new entity has been formed. This new company, named Gentec-EO USA, Inc., employs all the former Spectrum Detector employees, with Mr. Don Dooley as general manager. By creating this entity, Gentec Electro-Optics aims to strengthen its presence in the US.

Source: Photonics Online.

Based on their research, these sensors could be used for improving optical sources, detectors and modulators for optical interconnections and for creating biomolecules, such as plastic explosives for the Air Force.

Brongersma’s work is based on the unprecedented ability of nanometallic or plasmonic structures to concentrate light into deep-subwavelength volumes.

“Currently photodetectors, modulators and other chipscale devices are limited in their size by the fundamental laws of diffraction, but with plasmonics, we can make much more compact devices with one to two order of magnitude better performance parameters,” said Brongersma. “As the size of these devices determines their operation speed and power, it’s hard to make much more efficient devices.”

Maier has demonstrated plasmon waveguides on a silicon platform operating in the telecom band, and under AFOSR support he has realized some of the first plasmonic devices operating at THz frequencies.

“The telecom band is important since that’s where data communication is taking place by means of optical fibers and the Internet; the silicon platform is significant because most chips are made of that material,” said Maier. “THz frequencies are vital for their sensing of dangerous substances, including plastic explosives and anthrax.”

The study of plasmonics is bringing these scientists together as each works on fundamentals, information and biotechnology.

“Our team is working on demonstrating plasmon waveguides and cavities for a wide variety of applications spanning the electromagnetic spectrum from the visible to the microwave regime,” said Maier.

Brongersma’s group has worked on the basic concepts behind plasmonics-enabled light concentration and manipulation and is exploring a wide range of applications including faster computer chips, nanostructures synthesis, solar cells, water splitting using photoelectrochemistry, quantum optics and sensing.

Dr. Gernot Pomrenke, a program manager for the AFOSR Physics and Electronics directorate has overseen the research of these scientists for many years and Brongersma credits him with being one of the first program managers in the U.S. to realize the potential importance of plasmonics.

For their outstanding AFOSR-funded experimental and theoretical research in nano-plasmonics and nano-photonics, Brongersma and Maier were awarded the 2010 Raymond and Beverly Sackler Prize in the Physical Sciences.

“We are very excited that our fields of research have gained sufficient visibility for us to become the topics of such a prestigious prize, and we are excited and honored to share the prize equally,” said Brongersma.

The Sackler Prize in the Physical Sciences was established through the generosity of Dr. Raymond and Mrs. Beverly Sackler to encourage dedication to science, originality and excellence by awarding it to outstanding young scientists.

Source: NanoTechWire.

Details of compact 670 GHz circuit layout Approximately 30-nanometer Indium Phosphide T-gate

Developed at the company’s Simon Ramo Microelectronics Center under a contract with the Defense Advanced Research Projects Agency’s (DARPA) Terahertz Electronics program, this new performance record more than doubles the frequency of the fastest reported integrated circuit.

Dr. William Deal, THz Electronics program manager for Northrop Grumman’s Aerospace Systems sector, detailed the performance of this new TMIC amplifier today at the Institute of Electrical and Electronics Engineers’ (IEEE) International Microwave Symposium being held in Anaheim, Calif. He told fellow scientists that the TMIC amplifier is the first of its kind operating at 670 GHz.

“A variety of applications exist at these frequencies. These devices could double the bandwidth, or information carrying capacity, for future military communications networks. TMIC amplifiers will enable more sensitive radar and produce sensors with highly improved resolution,” said Deal.

His technical paper is available online.

The goal of DARPA’s Terahertz Electronics program is to develop the critical device and integration technologies necessary to realize compact, high-performance, electronic circuits that operate at center frequencies exceeding 1.0 THz. Managed by DARPA’s Microsystems Technology Office, the program focuses on two areas – terahertz high-power amplifier modules, and terahertz transistor electronics.

“The success of the THz Electronics program will lead to revolutionary applications such as THz imaging systems, sub-mm-wave ultra-wideband ultra-high-capacity communication links, and sub-mm-wave single-chip widely-tunable synthesizers for explosive detection spectroscopy,” according to Dr. John Albrecht, THz Electronics program manager for DARPA.

A transistor amplifier magnifies input signals to yield a significantly larger output signal. In 2007, Northrop Grumman set a new world record for transistor speed with an ultra-fast device to provide much higher frequency and bandwidth capabilities for future military communications, radar and intelligence applications.

The company produced and demonstrated an indium phosphide-based High Electron Mobility Transistor (InP HEMT) with a maximum frequency of operation of more than 1,000 gigahertz, or greater than one terahertz.

Source: EarthTimes.

“The interesting properties of graphene are all collective phenomena,” says Rotenberg, an ALS senior staff scientist responsible for the scientific program at ALS beamline 7, where the work was performed. “Graphene’s true electronic structure can’t be understood without understanding the many complex interactions of electrons with other particles.”

The electric charge carriers in graphene are negative electrons and positive holes, which in turn are affected by plasmons—density oscillations that move like sound waves through the “liquid” of all the electrons in the material. A plasmaron is a composite particle, a charge carrier coupled with a plasmon.

A theoretical model of plasmaron interactions in graphene, sheets of carbon one atom thick.

“Although plasmarons were proposed theoretically in the late 1960s, and indirect evidence of them has been found, our work is the first observation of their distinct energy bands in graphene, or indeed in any material,” Rotenberg says.

Understanding the relationships among these three kinds of particles—charge carriers, plasmons, and plasmarons—may hasten the day when graphene can be used for “plasmonics” to build ultrafast computers—perhaps even room-temperature quantum computers—plus a wide range of other tools and applications.

Strange graphene gets stranger

“Graphene has no band gap,” says Bostwick, a research scientist on beamline 7.0.1 and lead author of the study. “On the usual band-gap diagram of neutral graphene, the filled valence band and the empty conduction band are shown as two cones, which meet at their tips at a point called the Dirac crossing.”

Graphene is unique in that electrons near the Dirac crossing move as if they have no mass, traveling at a significant fraction of the speed of light. Plasmons couple directly to these elementary charges. Their frequencies may reach 100 trillion cycles per second (100 terahertz, 100 THz)—much higher than the frequency of conventional electronics in today’s computers, which typically operate at about a few billion cycles per second (a few gigahertz, GHz).

Plasmons can also be excited by photons, particles of light, from external sources. Photonics is the field that includes the control and use of light for information processing; plasmons can be directed through channels measured on the nanoscale (billionths of a meter), much smaller than in conventional photonic devices.

And since the density of graphene’s electric charge carriers can easily be influenced, it is straightforward to tune the electronic properties of graphene nanostructures. For these and other reasons, says Bostwick, “graphene is a promising candidate for much smaller, much faster devices—nanoscale plasmonic devices that merge electronics and photonics.”

The usual picture of graphene’s simple conical bands is not a complete description, however; instead it’s an idealized picture of “bare” electrons. Not only do electrons (and holes) continually interact with each other and other entities, the traditional band-gap picture fails to predict the newly discovered plasmarons revealed by Bostwick and his collaborators.

The team reports their findings and discuss the implications in “Observations of plasmarons in quasi-free-standing doped graphene,” by Aaron Bostwick, Florian Speck, Thomas Seyller, Karsten Horn, Marco Polini, Reza Asgari, Allan H. MacDonald, and Eli Rotenberg, in the 21 May 2010 issue of Science (“Observation of Plasmarons in Quasi-Freestanding Doped Graphene”).

Graphene is most familiar as the individual layers that make up graphite, the pencil-lead form of carbon; what makes graphite soft and a good lubricant is that the single-atom layers readily slide over one another, their atoms strongly bonded in the plane but weakly bonded between planes. Since the 1980s, graphene sheets have been rolled-up into carbon nanotubes or closed buckyball spheroids. Theorists long doubted that single graphene sheets could exist unless stacked or closed in on themselves.

Then in 2004 single graphene sheets were isolated, and graphene has since been used in many experiments. Graphene sheets suspended in vacuum don’t work for the kind of electronic studies that Bostwick and Rotenberg perform at ALS beamline 7.0.1. They use a technique known as angle-resolved photoemission spectroscopy (ARPES); for ARPES, the surface of the sample must be flat. Free-standing graphene is rarely flat; at best it resembles a crumpled bedsheet.

Using electrons to draw images of composite particles

“One of the best ways to grow a flat sheet of graphene is by heating a crystal of silicon carbide,” Rotenberg says, “and it happens that our German colleagues Thomas Seyller from the University of Erlangen and Karsten Horn from the Fritz Haber Institute in Berlin are experts at working with silicon carbide. As the silicon recedes from the surface it leaves a single carbon layer.”

Using flat graphene made this way, the researchers hoped to study graphene’s intrinsic properties by ARPES. First a beam of soft x-rays from the ALS frees electrons from the graphene (photoemission). Then by measuring the direction (angle) and speed of the emitted electrons, the experiment recovers their energy and momentum; the spectrum of the cumulative emitted electrons is transmitted directly onto a two-dimensional detector.
The result is an image of the electronic bands created by the electrons themselves. In the case of graphene, the picture is x shaped, a cross-sectional cut through the two conical bands.

The “bare electron” band-gap diagram of neutral graphene (right) shows the filled valence band and the empty conduction band forming two cones that meet at the Dirac crossing (arrow). But even low-resolution ARPES results (left) suggest that below the Dirac crossing, the energy and momentum distribution of charge carriers is not that simple.

“Even in our initial experiments with graphene, we suspected that the ARPES distribution was not quite as simple as the two-cone, bare-electron model suggested,” Rotenberg says. “At low resolution there appeared to be a kink in the bands at the Dirac crossing.” Because there really is no such thing as a bare electron, the researchers wondered if this fuzziness was caused by charge carriers emitting plasmons.

“But theorists thought we should see even stronger effects,” says Rotenberg, “and so we wondered if the substrate was influencing the physics. A single layer of carbon atoms resting on a silicon carbide substrate isn’t the same as free-standing graphene.”

The silicon-carbide substrate could in principle weaken the interactions between charges in the graphene (on most substrates the electronic properties of graphene are disturbed, and the plasmonic effects can’t be observed). Therefore the team introduced hydrogen atoms that bonded to the underlying silicon carbide, isolating the graphene layer from the substrate and reducing its influence. Now the graphene film was flat enough to study with ARPES but sufficiently isolated to reveal its intrinsic interactions.

The images obtained by ARPES actually reflect the dynamics of the holes left behind after photoemission of the electrons. The lifetime and mass of excited holes are strongly subject to scattering from other excitations such as phonons (vibrations of the atoms in the crystal lattice), or by creating new electron-hole pairs.

“In the case of graphene, the electron can leave behind either an ordinary hole or a hole bound to a plasmon—a plasmaron,” says Rotenberg.

Detailed ARPES results reveal that the energy bands of ordinary charge carriers (holes) meet at a single point, but conical bands of plasmarons meet at a second, lower Dirac crossing. Between these crossings lies a ring where the hole and plasmaron bands cross. The new band picture indicates how strongly plasmons couple to the charge carriers in graphene.

Taken together, the interactions dramatically influenced the ARPES spectrum. When the researchers deposited potassium atoms atop the layer of carbon atoms to add extra electrons to the graphene, a detailed ARPES picture of the Dirac crossing region emerged. It revealed that the energy bands of graphene cross at three places, not one.

Ordinary holes have two conical bands that meet at a single point, just as in the bare-electron, non-interacting picture. But another pair of conical bands, the plasmaron bands, meets at a second, lower Dirac crossing. Between these crossings lies a ring where the hole and plasmaron bands cross.

“By their nature, plasmons couple strongly to photons, which promises new ways for manipulating light in nanostructures, giving rise to the field of plasmonics,” Rotenberg says. “Now we know that plasmons couple strongly to the charge carriers in graphene, which suggests that graphene may have an important role to play in the merging fields of electronics, photonics, and plasmonics on the nanoscale.”

Source: NanoWerk.

“Up until now, THz diode has only been available as a discrete device. The integration of a discrete THz diode into a circuit assembly with other active and passive components required wire bonding. Although this approach was not desired, it was unavoidable for many millimeter-wave applications due to the lack of a monolithic solution,” commented Jerry Curtis, Chief Executive Officer of GCS. “Our engineering team has overcome the technical challenges by developing a planar Schottky diode process with THz performance. This fully monolithic process, with MIM capacitor, spiral inductor, thin film resistor and backside via features, is now offered as a standard foundry process. The THz diode process has been demonstrated as a mixer in a W-Band up-converter with a conversion loss of 6 dB, with a LO frequency of 91.8GHz (12 dBm) and an IF of 2.25 GHz. The process is ideal for applications in mm-wave frequency transceivers, as well as Terahertz imaging systems,” continued Mr. Curtis.

Source: ChipDesign.

Terahertz (THz) radiation is one of the hottest areas of modern physics research. This is because THz light waves, or T-rays as they are sometimes called, have great potential for spectroscopy and for the scanning of objects in a homeland security setting that are opaque to infrared and visible light.

The trouble is that THz light waves — which fall in the range of 0.3 to 10 trillion cycles per second or, equivalently, wavelengths of about 30 to 1000 microns — are difficult to make with traditional means. Now scientists at MIT have combined several technologies to obtain a versatile source of THz light.

They start with a quantum cascade laser (QCL) device, which differs fundamentally from a traditional semiconductor laser. In most traditional lasers, light comes from the recombination of an electron with a hole (a vacancy in the surrounding semiconducting material). But in a QCL device, light comes from the transition of an electron to a succession of ever lower energy levels in a series of layers in a sandwich-style structure of thin semiconducting layers.

This type of laser has a unique property: one electron (as it moves through the layers) triggers the release of many photons. The emitted light energy of the device can be changed by altering the thickness of the layers.

Population inversion is provided over a range of energies provided by the cascaded energy levels described above with the fine energy or wavelength selection provided by the laser cavity. In the MIT approach, tuning is achieved by changing the width of the laser light beam (and hence cavity) by precisely controlling the distance between a specially designed block material and the laser. This technique is analogous to changing the pitch of a guitar string by changing its diameter. In this case, the laser waveguide is much narrower than the wavelength of the light, hence the description of this setup as a “wire” laser.

Qi Qin of MIT says their cascade laser can be tuned continuously and controllably to produce terahertz radiation over a broad range. “At present, this is the only viable mechanism to achieve broad continuous tuning in terahertz quantum-cascade lasers,” says Qin.

Presentation CThU2, “Development of Tunable Terahertz Wire Lasers” by Qi Qin et al. is at 3 p.m. on Thursday, May 20.

Led by BU’s Richard Averitt, the team has developed a new way to detect and control terahertz (THz) radiation using optics and materials science. This type of radiation is made up of electromagnetic waves that can pass through materials safely. Their work may pave the way for safer medical and security scanners, new communication devices, and more sensitive chemical detectors.

Scientists and engineers have long sought devices that could control THz transmissions. Such a device would be a technological breakthrough because it would allow information to be sent via THz waves. Like X-rays, these waves can pass through solid materials, potentially revealing hidden details within. Unlike the ionizing energy of real X-rays, THz radiation causes no damage to materials as it passes through them.

The quest to create devices that emit or manipulate THz radiation is often referred to as a race to fill in the “THz gap,” since the frequency of THz radiation on the electromagnetic spectrum falls in between microwave and infrared radiation — both of which are already broadly used in communication.

This race has often stumbled right out of the blocks, however, because no technologies have proven able to effectively solve the basic problem of manipulating the properties of a beam of THz radiation. Now Averitt and his colleagues have made an important step in this direction by using an unusual class of new materials known as “metamaterials.”

Metamaterials are unusual in the way they interact with light, giving them properties that don’t exist in natural materials. They have grabbed headlines and captured the popular imagination in recent years after several groups of researchers have used metamaterials to achieve limited forms of “cloaking” — the ability of a material to completely bend light around itself so as to appear invisible.

Averitt uses these same sorts of metamaterials to interact with and change the intensity of a beam of THz radiation. His device consists of an array of split-ring-resonators — a checkerboard of flexible metamaterial panels that can bend and tilt. By rotating the panels, his team can control the electromagnetic properties of a beam of THz energy passing by them.

“The idea is that you can manipulate your terahertz beam by reorienting the metamaterial elements as opposed to reorienting your beam,” says Averitt.

Arrays of these metamaterial panels could potentially function as pixels on a camera that detects THz radiation, he says. Absorption of THz radiation would cause the panels to tilt more or less depending on the intensity of the THz bombarding them.

“One of the goals, from a technological point of view, is to be able to do stand-off imaging, to be able to detect things beneath a person’s clothes or in a package,” says Averitt.

Such detection applications, though, would require more powerful THz sources like quantum cascade lasers, which are under development — though great technological strides have been made in the last few years.

Presentation CtuF3, “Structurally Reconfigurable Metamaterials at Terahertz Frequencies,” by Hu Tao and Richard D. Averitt takes place Tuesday, May 18 at 8:30 a.m.

Source: EarthTimes.

The mobile scanner works on a test wall. A software system reveals the structure of the concealed paintings. Credit: Fraunhofer IWS

Many church paintings are hidden from sight because they were painted over centuries ago. In the 16th century, for instance, Reformation iconoclasts sought to obscure the religious murals, while in later times the iconoclast images often were painted over once again. Several layers of paintings from various epochs can now be found superimposed on top of each other. If mechanical methods are used to uncover these pictures there is always a risk that the original work will be damaged.

What’s more, the more recent layers and pictures on top of the original, which are also worthy of preservation, would be destroyed. Research scientists at the Fraunhofer Institute for Material and Beam Technology IWS in Dresden are now working on a non-destructive method for rendering these works visible, which involves the use of terahertz (THz) radiation. In the TERAART project funded by the German federal ministry of education and research (BMBF) they are cooperating with Dresden University of Technology, the FIDA Institute for Historic Preservation in Potsdam and the Dresden Academy of Fine Arts.

“We use THz radiation because it can penetrate the plaster and lime wash even if the layer is relatively thick. Unlike UV radiation for example, THz radiation does not damage the work of art. Infrared beams cannot be considered because they do not penetrate deep enough. Microwaves offer no alternative either, because they do not achieve the necessary width and depth resolution,” explains Dr. Michael Panzner, scientist at the IWS. A mobile system that can be used anywhere was developed to conduct the examinations. It consists of a scanner with two measuring heads which travels contactlessly over the wall. One measuring head transmits the radiation, the other picks up the reflected beams. The researchers were supported by the Fraunhofer Institute for Physical Measurement Techniques IPM, which built the adapted THz component.

“To produce the THz radiation we use a femtosecond laser incorporating the design principle of a fiber laser. The THz time domain spectroscopy technique applied by us utilizes the short electromagnetic pulses with a duration of just one to two picoseconds produced by the femtosecond laser. Each layer and each pigment reflects these pulses differently so that both a picture contrast as well as depth information can be obtained,” says Panzner. “The measured results provide information for example about the thickness of the layers, what pigments were used and how the colors are arranged. A specially developed software system puts the measured results together to form a picture displaying the structure of the concealed paintings.”

On a test wall, on which paintings in various types of paint were painted over with distemper, the scientists have already succeeded in revealing the structures of the concealed pictures. The next step will be to conduct a practical test in a church. The experts are also confident of being able to use THz radiation to detect the presence of carcinogenic biocides on and in works of art made of wood or textiles. “Preservationists will be very interested in our reveal-all-scanner for works of art,” affirms Panzner.

Source: PhysOrg.com.

Toptica is a global market leader for THz sources and their applications, offering laser-based time and frequency domain sources. Part of Toptica’s portfolio is offering customers a THz Standard Package plus Spectroscopy Kit product which uses a coherent detection technique for continuous wave (“cw”) THz signals. Under the terms of the Licensing Agreement, T-Ray will collect royalties on the sales of this product in the United States.

“The quality of Toptica’s products and their expertise in the field of THz imaging are world class,” said Thomas Braun, CEO of T-Ray. “This is a significant endorsement of T-Ray’s cw THz platform technology. While T-Ray continues to focus on developing its own skin cancer imaging device, we are forecasting additional Licensing Agreements to be concluded this year, positioning the Company for accelerated growth.”

T-Ray’s platform THz imaging technology has been shown to have numerous potential applications including homeland security, the detection of explosives and ceramic knives; process control in the paper, plastics, petro chemical and pharmaceutical industries; and medical imaging for detection of skin and other cancers. THz waves are also a safe, accurate, and economical alternative to other scanning methods such as high frequency ultrasound, magnetic resonance imaging, and near-infrared imaging. This emergent technology has the potential to revolutionize the way many diseases are diagnosed, and ultimately cured. Numerous studies have shown that THz imaging can be used to image various cancers which continues to be the focus of T-Ray’s skin cancer imaging research and development.

One of the main sources of THz radiation, the interdigitated photoconductive antenna, can now be ‘tuned’ to THz frequencies that were previously difficult to reach. Researchers at the Ecole Normale Supérieure in France found that changing the spacing between the electrodes in the antenna’s structure enables the emission spectrum to be centred at a chosen frequency; a property that will be useful for spectroscopy and imaging, where access to particular parts of the THz spectrum is needed.

The generation gap

There are many possible applications in the THz range (0.1-10 THz) including explosives and drugs detection, medical imaging, gas detection, high-speed communications and fundamental studies of the physics of materials or very low energy systems (1 THz~4 meV). However, despite intense research efforts, there have been many challenges that have not yet been overcome in achieving a miniature, efficient THz source. Today’s research is mainly focused on a variety of different compact optoelectronic devices like photoconductive antennas (PCAs) which operate at room temperature but need an external laser excitation, or THz quantum cascade lasers which are powerful but currently operate at cryogenic temperatures. PCAs have been used and studied as a source of THz radiation for over 20 years. One of the most efficient is the interdigitated PCA with its electrode comb geometry which radiates in the THz range when illuminated with, typically, an infrared femtosecond pulsed laser. They are now increasingly being used in laboratory applications as they radiate with broadband emission and high power; they suffer little from diffraction effects as the illuminated surface area is large; and they operate at low electrical input power.

A selective response

The team at Ecole Normale Supérieure have been developing and using interdigitated PCAs as a pulsed source for studies with a THz time-domain (TDS) setup which is used to probe physical or chemical properties related to low energy interactions within materials or compounds. They have been studying the geometry of interdigitated PCAs in order to understand their mechanisms better and therefore create more efficient THz sources. In their most recent investigation, they found that the emitted spectral peak frequency increased from 0.73 to 1.33 THz as the spacing between the electrodes in the structures was decreased from 20 to 2 ?m. This result enables the frequency response of an interdigitated PCA to be selected by the design of its electrode spacing geometry. A big challenge that the team faced to achieve this result was the fabrication of the devices with the electrode spacing on the micron level as the standard UV contact lithography technique starts to reach its limits. They overcame this by optimising the processing procedure and the team next plan to develop interdigitated PCAs to cover the high frequency part of the THz range using the same laser source. “This could be achieved by further reducing the electrode spacing of the interdigitated structure but it will need a different lithography technique,” said Julien Madéo, a researcher at Ecole Normale Supérieure. “We are also investigating new interdigitated geometries with different patterns to achieve higher frequency emission.”

Future improvements

With worldwide research efforts underway to achieve more efficient THz sources, the team predict that the use of PCAs as THz sources will rapidly progress as a better understanding is developed from experiments and simulations. “We believe that electromagnetic simulations of these devices will continue to be important and allow the antenna geometry to be adapted to the required spectral range,” said Madéo. “Another challenge though is that these structures exhibit a weak efficiency (< 1%), and high power and expensive pulsed lasers are needed to produce relatively strong THz electric fields. We will need to think about new geometries and new materials to improve these issues, possibly combined with the use of cheaper and compact fibre-based laser systems. Improving these types of sources will permit the THz technological range to become mature and comparable to those used in microwave electronics and infrared optical systems.”

The Letter presenting the results on which this article is based can be found on the IET Digital Library.
For further reading, please visit www.lpa.ens.fr
Source: IET.

The article examined experimental results from a video-rate device. The device uses terahertz (THz) rays that emit a continuous narrow bandwidth radiation of 0.1 (THz). The instrument creates a two-dimensional image of a point in an object. The image is reconstructed at a rate of 16 milliseconds per frame with a four-element detector array. The number of detectors, the configuration of the detection array and how well the baselines are calibrated affects the image resolution and quality.

“Scientists favor terahertz radiation because it can transmit through most non-metallic and non-polar mediums,” said Federici. “When a terahertz system is used correctly, people can see through concealing barriers such as packaging, corrugated cardboard, walls, clothing, shoes, book bags, pill coatings, etc. in order to probe for concealed or falsified materials.”

Once the rays penetrate those materials, they can also characterize what might be hidden – be they explosives, chemical agents or more – based on a spectral fingerprint the rays will sense which can identify the material. terahertz radiation also poses minimal or no health risk to either the person being scanned or the THz system operator.

At this time, instruments using terahertz imaging are widely used in laboratories and have shown some limited use in commercial applications. However, a THz imaging system for security screening of people has not yet reached the market. Researchers say that such a system is at least five years away. The NJIT device, however, has great promise. According to Federici, THz imaging systems have an inherent advantage over millimeter wave imaging systems due to the intrinsically improved spatial resolution that one can achieve with the shorter wavelength THz systems (typically 300 micrometer wavelength) compared to longer wavelength millimeter wave systems. However, video-rate THz imaging systems are not as well advanced as their millimeter wave counterparts.

One technical limitation in developing video-rate THz imaging is the cost of THz hardware components including detectors. Consequently, THz imaging systems create images using a very small number of detectors in contrast to the million or more detectors that are used in digital cameras. According to Federici, one can use advanced imaging techniques, such as synthetic aperture imaging methods, to compensate for the relatively few number of THz detectors in an imaging system.

“The idea has been to apply different methods of imaging with radio waves, where many of the ideas for synthetic aperture imaging originated, to terahertz rays,” said Federici. His research team has focused in particular on applications of synthetic aperture imaging to the terahertz range. “The advantage of this particular method is the ability to generate terahertz images with a large number of pixels using a limited number of terahertz detectors. This imaging method should also be capable of video-rate imaging, thereby enabling the real-time monitoring of people hiding concealed explosives or other dangers.” A typical imaging system would be analogous to a still or video camera designed for this purpose.

In 2005, Federici and his research team received a U.S. patent for a terahertz imaging system and method that enables video-rate THz imaging with a limited number of detectors. Since 1995, terahertz imaging has grown in importance as new and sophisticated devices and equipment have empowered scientists to understand its potential. The U.S. Department of Homeland Security, the Army Research Office, Department of Defense, and the National Science Foundation support Federici’s work.

While researchers have focused on the potential applications of terahertz rays for directly detecting and imaging concealed weapons and explosives, they say another application is the remote detection of chemical and biological agents in the atmosphere.

Source:
New Jersey Institute of Technology
and MedicalNewsToday.

Thanks to a range of developments in technology, systems based on terahertz technology are poised to enter and create significant new markets within the decade. A recently published market study by Thintri, Inc. highlights significant commercial opportunities in terahertz technology this decade. Of the many potential applications of terahertz radiation, manufacturing is potentially the most promising.
The terahertz portion of the electromagnetic spectrum is vaguely defined but is basically the band between infrared and microwave radiation, usually considered to run from 300 GHz to perhaps 10 THz, overlapping those bands commonly referred to as submillimeter and far infrared.

Terahertz radiation is a critical concern in astronomy, given that approximately one half the total luminosity of the universe and 98% of the photons emitted in the history of the universe lie in the terahertz portion of the spectrum, and that terahertz waves are not scattered by gas clouds in space.

Terahertz waves are reflected by metallic surfaces and absorbed by water, both of which remain opaque to terahertz signals. However, most other materials are transparent to terahertz radiation, to varying degrees. Terahertz systems can provide both images and spectroscopic data, (possibly in the same measurement), and ranging data that can measure coating or layer thicknesses, even in structures of many layers.

A number of technical breakthroughs in photonics, electronics and nanotechnology have occurred since the early 1990s which have brought terahertz technology within striking distance of significant commercial markets like security, communications, nondestructive evaluation, medicine and electronics. Bulk and ease of use have been longstanding issues with terahertz technology, but recently developed systems are as easy to use as an oscilloscope, and some are so small and robust that they can be delivered through the mail.

While development continues on components, attention is shifting to development of applications that are now ready to take advantage of the extraordinary versatility of the terahertz band. Indeed, application and market development are now the primary hurdles in the way of creation of significant markets for terahertz systems in such promising applications as manufacturing.

Terahertz technology has been promoted for an astonishingly wide range of applications:

Manufacturing: real-time, in-situ process control, product inspection and material evaluation
Food: food inspection for spoilage and contamination, determining the water content of food
Biomedicine: mammography, bone tomography, endoscopy, medical diagnostics, detection of skin cancer and other diseases, identification of drugs or other substances in the blood, genetic sequencing
Security and defense: detection of concealed weapons and explosives; evaluation of biological threats; airline passenger screening; detection of contraband in luggage, shipping containers; inspecting or reading unopened mail
Imaging: imaging the contents of packages, sealed documents or closed books, fossils or oil encased in rock
Scientific: environmental sensing, pollution detection, plasma diagnostics, chemistry and biochemistry
And many more.
Terahertz radiation’s main advantage is its ability to penetrate an extraordinary range of materials. It has been used to image through drywall to locate studs and wiring; to peer inside a closed bottle of tablets to ensure their quality without disturbing the contents; to measure the moisture content of packaged cigarettes; to image through plastic, paper, cardboard and most common fabrics.

Continue reading full article at IndustryWeek.com.

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“The collaboration with the University of Leeds could lead to low cost, compact and easy to use THz diagnostic and imaging systems for applications in medical imaging, explosives detection, airport security, and manufacturing quality control,” said Thomas Braun, President and CEO of T-Ray Science. “We are honoured to have the opportunity to work with a world class university in developing this cutting edge technology. T-Ray is a natural industrial partner for the University of Leeds as we hold the exclusive license from MIT (the Massachusetts Institute of Technology) for the CW coherent detection system. Our collaboration with the University of Leeds compliments our other collaborations with the University of Victoria, the University of Sherbrooke and the University of Manitoba, all aimed at lowering the cost and increasing the power of existing THz diagnostic and imaging systems.”

The University of Leeds received a grant from the Engineering and Physical Sciences Research Council of the United Kingdom to fund a project to develop a low cost, pulsed and continuous wave (“CW”), fibre coupled terahertz (THz) spectrometer which operates at telecoms wavelengths. T-Ray supported the grant application and will assist in the project through laboratory tests of the newly developed system. The Company will also have the opportunity to license any Intellectual Property that may result from the project.

T-Ray owns the exclusive license from the Massachusetts Institute of Technology for the only known CW coherent detection system which was invented by Drs. Simon Verghese and Alex McIntosh. The CW system being developed by Leeds will produce continuous THz waves at a fixed frequency for a very low cost and will be more compact and robust because of the use of mass produced diode lasers, rather than the large and expensive Ti:Sapphire lasers traditionally used by THz researchers.

Source: FoxBusiness.com.

Under the Collaboration Agreement, SAIC-Frederick’s Biopharmaceutical Development Program will assess Applied & Research Photonics’s T-ray technology for identifying chemical compounds in materials related to cGMP manufacturing.

The agreement was formed under NCI’s Advanced Technology Partnerships Initiative (ATPI), which aims to reduce the time and cut the cost of translating basic research into new preventive measures, diagnostic tests, and effective, patient-specific treatments for cancer patients. SAIC-Frederick is facilitating these partnerships.

The collaboration will focus on applications of time-domain terahertz spectroscopy to identify chemical compounds. SAIC-Frederick, as part of its normal function for biopharmaceutical development, explores alternatives to traditional methodologies used to support the development of new agents.

“We are very pleased to provide the terahertz capabilities in helping the NCI’s efforts in fighting cancer. With its parts-per-trillion sensitivity, we are confident that the TeraSpectra will make a significant contribution to NCI’s mission,” said Anis Rahman, CTO of ARP. He also added, “Presence of residuals in drug formulations is a major source of post-treatment toxicity. Current methods are not sensitive enough to detect a very small amount of residuals left in the drug candidates from the process chemistry. Since terahertz offers very high sensitivity at very low concentrations, it is expected that application of this tool will help solve some critical problems involving the identification and quantification of the residuals in biopharmaceutical products for cancer treatment.”

For information on NCI’s Advanced Technology Partnerships Initiative, see: ATPIhome.com, and for Applied Research & Photonics see: arphotonics.net.

info@arphotonics.net

Alexey Belyanin focuses his research on terahertz, otherwise known as THz or T-rays, which he says is the most under-developed and under-used part of the electromagnetic spectrum. It lies between microwave radiation and infrared (heat) radiation.

Belyanin, associate professor in the Texas A&M Physics and Astronomy Department, has collaborated with colleagues at Rice University and the National High Magnetic Field Laboratory to publish findings about their T-ray research in the renowned journal Nature Physics.

“THz radiation can penetrate through opaque dry materials. It is harmless and can be used to scan humans,” Belyanin says. “Unfortunately, until recently the progress in THz technology has been hampered by a lack of suitable sources and detectors.”

Belyanin and his team have offered hope: The researchers are able to control the T-rays by varying external parameters like temperature or magnetic field, making it possible to build THz sensors, cameras and other devices.

Traditionally, powerful photons from visible or near-infrared laser pulses are used to probe semiconductors, knocking electrons out of the atoms. Belyanin and collaborators use the less powerful T-rays instead, which only excite the waves in the electron gas because T-rays do not have enough energy to knock out electrons.

“This is as if instead of throwing a stone into a tank of water, which would create a lot of splashes, we gently vibrate one wall of the tank, sending a sound wave through the body of water and ripples over its surface,” he explains.

By varying temperature and the magnetic field, scientists can tune the pulses and observe the behavior of the waves.

“This provides extremely valuable and unique information about the properties of the material, just like seismic waves tell you what is in the Earth’s interior,” the Texas A&M physicist points out.

“The highlight of our results is observations of interference of magnetoplasmons. By tiny changes in the applied magnetic field or temperature, we can make plasma waves amplify or cancel each other. This makes the whole sample either completely opaque or transparent to the incident THz radiation.”

Belyanin believes the technology has important practical implications, such as in security work.

“Using THz cameras, we could detect weapons or drugs concealed on a human body, or look inside envelopes and boxes,” he says. There are many other applications for THz radiation, including material studies, chemistry, biology, medicine.”

Source: tamu.edu

In The Truth About Santa: Wormholes, Robots and What Really Happens on Christmas Eve, author Gregory Mone explains the elaborate systems that make it all possible.

“I think part of the reason people look at Santa and say it’s all magic, is that his job does seem impossible, this notion of getting around the world and visiting all these homes in a single night,” Mone, an editor at Popular Science magazine, tells NPR’s Renee Montagne.

But Santa’s secret, Mone says, is that he uses tools that are hundreds of years beyond what we have at our disposal.

“As a result, it does seem like magic,” he says. “But it’s really all science and technology.”

For instance, Santa’s red suit: It’s designed for the extreme conditions he encounters while traveling at warp speed and bending space and time. And, Mone says, “Santa’s suit is laden with what are called metamaterials, which have the effect of bending light around a person so that they turn invisible” — which can come in handy if there are curious children peeking during his Christmas deliveries.

Santa’s reading glasses, which contribute to his quaint image, are actually equipped with what’s called a “heads-up display.” When Santa looks through the lenses, he sees a range of information about the residents of the house he’s visiting, the presents to leave, directions to the next house and more.

He also has a special device to ensure he doesn’t double up on presents under the tree.

“Santa knows what we want, but he doesn’t really know what presents to leave for a given kid until he gets to the house and looks under the tree,” Mone says.

But Santa doesn’t have time to unwrap and rewrap all the presents. So he uses a terahertz wave radiation scanner to see through the wrapping and make out the shape inside, indicating which toys are already under the tree. That way, he can leave a different one.

The latest research in the social sciences has also had an effect on Santa’s operations. Mrs. Claus, who’s particularly fond of the works of Harvard University child psychiatrist Robert Coles, convinced Santa that positive reinforcement would be more powerful in altering the behavior of “naughty” children.

Because of this, Santa no longer leaves coal in their stockings.

From National Public Radio. Go to this site to listen to the entire radio story!

But practical ways to generate terahertz rays have been hard to find. Traditional gas lasers can operate in the right frequency band, but they’re big, expensive, and power-hungry. Semiconductor lasers — the kind you find in a DVD player — are small and cheap, but they’re hard to nudge out of a limited spectral range: consider how long it took to get from the infrared lasers of the first CD players to the blue lasers of Blu-Ray discs.

In 1994, researchers at Bell Labs invented a new kind of small but powerful semiconductor laser called a quantum cascade laser, and in 2002, it was shown to be able to operate at terahertz frequencies. But accurately assessing an object’s chemical composition requires exposing it to a continuous range of frequencies, which are absorbed to different degrees.

In a paper appearing in the most recent issue of Nature Photonics, Qing Hu, a professor of electrical engineering at MIT’s Research Laboratory of Electronics, and his colleagues describe the first practical method for tuning terahertz quantum cascade lasers. What’s more, the method is a fundamentally new approach to laser tuning that could have implications for other emerging technologies.

“Since the very beginning of terahertz development in the 1970s, people have been trying to make [high-power] sources that are compact and tunable, and so far, this is really the first example of such a source,” says Peter Siegel, who leads the Submillimeter Wave Advanced Technology group at NASA’s Jet Propulsion Laboratory at Caltech. “Qing deserves a lot of credit for all the work he put in and the groundbreaking ideas he pioneered and pushed through despite lots of setbacks and competition from other groups. He really, in the end, came through with a fantastic breakthrough.”

Tuning an ordinary semiconductor laser usually requires changing the length of its light-emitting cavity; occasionally, if the laser doesn’t need a broad frequency range, heating or cooling it will work instead. Hu compares these two approaches to changing the pitch of a guitar string by pressing down on it — changing its length — or screwing its tuning peg — changing its tension. Neither approach, however, works very well with terahertz quantum cascade lasers.

A third way to change the pitch of a guitar string, however, is to change its diameter: the lower-pitched strings on a guitar are thicker than the higher-pitched ones. And Hu’s tuning technique is, roughly speaking, to change the diameter of the light beam.

A light beam traveling through space can be thought of as a wave, undulating up and down indefinitely until it strikes a physical object. But when the same light beam is confined — in, say, an optical fiber or a long, thin, quantum cascade laser — it exhibits an electromagnetic-field pattern called a “transverse mode.” The transverse mode is kind of like another wave that’s perpendicular to the first one, except that it dies off very quickly — its undulations rapidly get smaller — as it gets farther from the light beam. In fact, its undulations die off so quickly that it can be thought of as simply one big undulation perpendicular to the light beam but centered on it.

Hu’s new tuning technique requires a particular type of quantum cascade laser called a wire laser, where the wavelength of the transverse mode — the width of the one big undulation — is actually greater than the width of the laser itself. Bringing a block of another material close enough to the laser deforms the transverse mode, which in turn changes the wavelength of the emitted light. In experiments, Hu and his colleagues found that a metal block shortened the wavelength of the light, while a silicon block lengthened it. Varying the proximity of the blocks also varies the extent of the shift.

Terahertz quantum cascade lasers have one big drawback: they need to be cooled with liquid nitrogen to very low temperatures. But Jerome Faist of the Swiss Federal Institute of Technology in Zurich, one of the inventors of the quantum cascade laser, says that while a room-temperature version is a difficult and long-term project, “nothing actually tells us it is impossible.” And Siegel adds that, with Hu’s tuning technique, “I don’t see why it would matter what temperature the laser was operated at.”

Hu points out that his technique could also be applied to a new type of tiny laser that can be used for extremely fine-scale sensing. Ordinarily, visible-light lasers cannot be narrower than the wavelength of the light being used, but researchers have found ways around that fundamental limit by using a virtual particle called a plasmon, which is like a wave passing through a cloud of electrons. Some new types of plasmon lasers could also be tuned through manipulation of their transverse modes.

In its experiments, Hu’s group used a mechanical lever to bring a block of either silicon or metal close to a quantum cascade laser from a single direction. But they’ve designed and are now building chips that would use electronically controlled microelectromechanical devices to bring the silicon and metal blocks in from different directions, giving the laser a precise and continuous tuning range from short to long wavelengths.

Source: R&D Magazine

The finding by Kono, a professor in electrical and computer engineering, former graduate student Xiangfeng Wang and their colleagues helps close a knowledge gap in the electromagnetic spectrum between the ranges that address electronic and photonic devices.

Their paper is published in the online version of the journal Nature Physics. Co-authors include Texas A&M theoretical physicist Alexey Belyanin, Los Alamos National Lab physicist Scott Crooker and Daniel Mittleman, a Rice professor in electrical and computer engineering.

Kono’s team had been studying the conductivity of indium antimonide. “This is a classic material people started working on in the 1940s,” he says. “It’s a typical semiconductor, and if you dope it, it’s highly conductive. But if you apply a magnetic field, it becomes an insulator, and that’s what we planned to look at.”

When Wang used terahertz spectroscopy to study the material, its unusual properties became apparent. “He started tuning various parameters-the magnetic field, temperature and then the frequency-and found that the terahertz transmission of the material changed drastically,” says Kono. “It went from opaque to transparent.”

They found that in a magnetic field, the doped indium antimonide, a solid-state plasma, transmitted circularly polarized waves that interfered with each other. This affected terahertz beams in much the same way polarized sunglasses interfere with visible light. To their surprise, at particular combinations of settings, the beams would pass right through.

“Terahertz is an exciting field right now,” says Kono. “This frequency range is considered to be the last frontier of the electromagnetic spectrum.”

Kono says neither type of semiconductor device in common use today-photonic and electronic-works in the terahertz range. “Photonic devices work in the visible and near-infrared ranges and electronic devices work in the kilohertz, megahertz and gigahertz ranges. There’s a clear gap where there’s no mature solid-state technology. That’s why a lot of people are working to fill it.”

“I wouldn’t say the terahertz region is unexplored, but it’s less so,” says Mittleman, who specializes in terahertz technologies and worked on the development of a terahertz version of Rice’s famous single-pixel camera. “There are some open problems that people haven’t thought about–or have thought about, but haven’t found good solutions for. The whole technology base is a lot less mature.”

Kono says applications for terahertz technology include imaging, spectroscopy and communications, and having a device that can serve as a terahertz switch would be a step forward.

Still, there are hurdles to making the lab’s discovery practical, one being the operating temperature. Wang worked with the indium antimonide at temperatures between 2 and 240 K.

“The temperature is certainly a concern,” Mittleman says. “If it’s going to have impact as a useful device for controlling terahertz beams, there is some work yet to do. I don’t think that’s impossible, but the route is not immediately clear.

“There’s not a lot of shocking new physics here,” he says, but the combination of techniques used to treat the indium antimonide made for interesting science. “People are going to think it’s pretty cool.

“I think it’s nice to find things like this, because it’s a great example of an unexpected discovery that could turn out to be really useful.”

Source: Rice University and LaboratoryEquipment.com

This near-field tip couples together with the data acquisition system “AixScan” also from AMO GmbH for the recording of time-domain THz signals at low noise levels. The sensor is dedicated for use in experimental or commercial fs pump-probe systems. The patent-pending tip design allows simple usage and minimum dielectric loading on the device under test.

About AMO GmbH

AMO, founded in 1993, is a privately owned company in Aachen, Germany, spin-off from the RWTH Aachen University. AMO is dedicated to micro- and nanofabrication technology, nanoelectronic and nanophotonic devices and high-end test and measurement systems. AMO combines semiconductor based process technology with modern electronic solutions for custom oriented high end solutions in test & measurement.

Research Capital Corp. has been engaged on a best efforts basis to raise up to $1.5 million. McCullough O’Connor Irwin LLP acts as legal counsel to T-Ray while Morton & Company acts for the agent.

Vancouver based T-Ray Science, Inc. is a device-to-system technology development company involved in the design, innovation and commercialization of THz electromagnetic radiation. The company ultimately seeks to revolutionize the way skin cancer is diagnosed and treated.

T-Ray currently has the following THz products at various stages of development towards commercialization: Photonics Chips, Photonic Circuit Chip Holder, Dual Mode Spectrometer, Skin Cancer Detector, and Whispering Gallery Mode Resonator (WGMR).

The new “memory metamaterials”, made by Tom Driscoll of the University of California at San Diego and colleagues, can have their electromagnetic properties temporarily modified depending on the level of applied voltage or light. According to the researchers, such tuning could allow for a “set-and-forget” approach to complex metamaterials for applications where it is impractical to maintain an external stimulus.

Harry Potter physics
Metamaterials are engineered structures that respond to electromagnetic waves in unusual ways. For example, they can be designed to have a refractive index that varies throughout, even taking on a negative value in some cases. This particular ability of metamaterials led to them being used in 2004 to make the first super-lens, which can beat the so-called diffraction limit, and the first invisibility cloak for microwaves in 2006.

One of the problems with most metamaterials is that they can only be designed to operate at a single “resonant” frequency. Although there are “frequency agile” metamaterials that allow their resonant frequency to be tuned with a certain stimulus, the tuning is lost as soon as the stimulus is taken away. Driscoll ‚Äì whose group includes others from San Diego, Duke University in North Carolina, US, and ETRI in Daejeon, South Korea ‚Äì solves this issue by creating memory metamaterials that can remember the new frequency that they should operate at.

Like many other metamaterials, memory metamaterials contain an array of conductive rings, called split-ring resonators (SRRs), which provide the basic electromagnetic properties. However, in memory metamaterials the SRRs are patterned onto vanadium dioxide, which has a metal-to-insulator phase transition that can be controlled with light or an applied voltage.

A new phase
It is the phase of vanadium dioxide, which can last for long periods after the light or voltage is withdrawn, that provides the “memory”. The specific phase alters vanadium dioxide’s capacitative properties, which in turn control the SRRs’ resonant frequency. Until the phase changes back, the resonant frequency is set.

To test their memory metamaterials, Driscoll and colleagues examined them with terahertz spectroscopy before and after they applied an electrical pulse. They found that the resonant frequency shifted from 1.65 THz by as much as 20%, and persisted for at least 10 minutes. “Such persistent tuning is likely to be useful in reconfigurable metamaterial devices, enabling a kind of set-and-forget approach to the reconfiguration process,” says Driscoll.

The researchers suggest that materials other than vanadium dioxide could push the effect to higher frequencies, and perhaps even the visible part of the spectrum.

This research was published in the latest edition of Science.

Source: Physics World.

The T-Ray((R)) 4000 uses optical fiber coupled terahertz sensors to generate 2D and 3D images for the detection of thickness, density, moisture content, delamination and structural health. Picometrix terahertz systems have been used to perform non-destructive testing on ancient artwork, pipeline repairs, ground based and aircraft radomes, integrated circuits, and the Space Shuttle. Now all of these inspections can be performed more quickly.

Dr. Matt Reid at the University of Northern British Columbia is using the new kilohertz T-Ray((R)) 4000 to provide cost savings and process control in the wood processing industry. His work is being conducted in conjunction with the College of New Caledonia, the Ministry of Forests and Range, and Del-Tech Manufacturing.

Source: PRNewsWire.

“The terahertz regime has become of particular interest simply because it may allow us to look into materials in a completely new way,” Diego Kienle tells PhysOrg.com. “This regime, which lies between microwave and optical frequencies is known as the terahertz gap. What one would like to have are devices which can operate – simply speaking – within this intermediate regime of conventional electronics and photonics.”

Kienle is a researcher at Sandia National Laboratories in Livermore, California. Along with François Léonard, also at Sandia, Kienle developed a theoretical model allowing scientists to simulate the response of carbon nanotube transistors at very high frequencies up into the terahertz (THz) regime. What they found may provide a basis for moving forward on a fundamental level, as well as in the development of new applications. “We wanted to know how carbon nanotubes behave in the terahertz frequency regime,” Kienle explains. He also points out that he and Léonard are interested in discovering whether such a regime could be helpful in “exploiting nanoscale devices.” The results of the exploration can be found in Physical Review Letters: “Terahertz Response of Carbon Nanotube Transistors.”
“Our objective was meant to investigate the possibilities for materials such as nanotubes to be useful some day to build practical devices that make use of the terahertz regime,” Kienle says. “You can get an idea of why there is such a growing interest to work on that topic, since it would provide a useful connection between what we have now in conventional electronics and optics thus closing the terahertz gap.”

Kienle believes that some of the possible applications of such nanoscale devices include transistors that can operate at faster speeds, improved tools for imaging and diagnosis of tissue in the medical and biological fields, advancements in molecule identification, and security screening. “Being able to study the terahertz regime is certainly interesting from a mere scientific perspective as well, since it would give us further insight into the dynamical aspects how electrons interact with external time-dependent fields on the nanoscale,” Kienle continues.

Kienle and Léonard used the computer to solve the quantum transport equations, which allow them to assess the frequency characteristics of different materials. “One important characteristic of such devices is to efficiently interact with externally applied fields.They have to be able to ‘respond’ — so to say — to ‘talk’ to signals in the terahertz regime.”

After running the model, it appears that carbon nanotubes would make good candidates for building devices capable of operating in the terahertz regime. “So far, from a theoretical viewpoint, it looks good, even though many more aspects, which have not been considered, still have to be investigated,” Kienle says. “It appears that using devices of nanoscale size could help us access the terahertz regime more easily.” He also points out that the computer modeling method he and Léonard used could also evaluate other materials. “Our approach is quite general and is useful for more than just carbon nanotubes,” he insists. “We can apply it to any other material class to identify qualitatively whether other types of materials show promise to be useful in a variety of applications.”

The next step is actually experimenting with materials that clear the modeling process. “This is a big practical challenge,” Kienle admits. “Building devices with nanometer dimensions and that work in the terahertz regime, specifically at room temperature, is very difficult to realize in practice, and may require further development of experimental techniques to breach into this regime. This may be a few years down the road, but there are few experimental groups that have begun performing terahertz measurements in these nano devices, although still at low temperatures.”

Kienle believes that the need for devices with new functionality in the terahertz regime will be in demand in the future, if one succeeds to built such devices. “Our technique would help investigate a number of nanoscale materials in order to make a sound evaluation of whether they would be useful at some point. We still have long ways to go to make it really work, but if one can do it this would be a big advancement and impact for this research field.”

Diego Kienle, François Léonard, “Terahertz Response of Carbon Nanotube Transistors,” Physical Review Letters (2009).

By Miranda Marquit. Source: PhysOrg.com

1. A highly sensitive and frequency tunable terahertz detector based on a carbon nanotube (CNT) quantum dot (QD).

Observations have been made of electron tunneling via terahertz-photon detection, called photon-assisted tunneling. This result means that the CNT-QD structure can be utilized as a frequency tunable terahertz detector. CNT-QD detector functions properly up to approximately 7 K. Higher-temperature operation of the CNT-QD terahertz detector is also possible with more refined fabrication techniques.

The next important step is to improve detector performance in two important ways: sensitivity and frequency selectivity. A much more sensitive readout of the terahertz-detected signal could be achieved by capacitively coupling a CNT-QD with a quantum point contact device on a GaAs/AlGaAs heterostructure, which makes it possible to observe single-electron dynamics. And frequency selectivity could be improved by using a double-coupled CNT-QD, in which photon-assisted tunneling takes place as a result of electron transitions between two well-defined discrete levels.

2. A near-field terahertz detector for high-resolution imaging.

Contrary to the situation in the microwave and visible-light region, the development of near-field imaging in the terahertz region has not been well established. Japan RIKEN has developed a new device for near-field terahertz imaging in which all components—an aperture, a probe, and a detector—are integrated on one gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs) chip. This scheme allows highly sensitive detection of the terahertz evanescent field alone, without requiring optical or mechanical alignment.

Two approaches can be used to achieve high spatial resolution in optical imaging: a solid immersion lens and near-field imaging. Though we have previously constructed a terahertz imaging setup based on a solid immersion lens, its resolution is restricted by the diffraction limit.3 A powerful method for overcoming the diffraction limit is the use of near-field imaging. This technique has been well established in visible and microwave regions using either a tapered, metal-coated optical fiber or a metal tip, and either a waveguide or a coaxial cable. However, the development of near-field imaging in the terahertz region has been hindered by the lack of terahertz fibers or other bulk terahertz-transparent media suitable for generating near-field waves, as well as the low sensitivity of commonly used detectors in the terahertz region.

In conventional near-field imaging systems, the propagation field arising from the scattering of the near-field (evanescent) wave is measured with a distant detector, which requires detecting very weak waves (and the influence of far-field waves is unavoidable). In contrast, our near-field terahertz imager places the aperture, probe, and detector in close proximity. The 8-µm-diameter aperture and planar probe, each of which is insulated by a 50-nm-thick silicon dioxide (SiO2) layer, are deposited on the surface of a GaAs/AlGaAs heterostructure chip.

An optical micrograph (left) and a schematic representation (right) shows the design of a highly sensitive on-chip near-field THz detector. The 8-µm-diameter aperture and planar metallic probe, each of which is insulated by a 50-nm-thick silicon dioxide (SiO2) layer, are deposited on the surface of a GaAs/AlGaAs heterostructure chip. (Courtesy of RIKEN)

Because integration with the CNT-QD detector requires improvements in the device fabrication process (specifically, by using higher-performance electron-beam lithography equipment), a two-dimensional electron gas (2DEG)—located only 60 nm below the chip surface—is used as the terahertz detector.

Why Terahertz Detection is Tough

The photon energy of the terahertz wave, on the order of millielectron volts (meV), is two to three magnitudes lower than that of the visible light, making the development of a high-performance terahertz detector a difficult task. Another problem with terahertz detection is low spatial resolution of terahertz imaging, which results from the longer wavelengths of terahertz radiation compared to that of visible light.

Source: NextBigFuture.com

ARP uses dendrimer based terahertz generation technique via difference frequency method. This technique is different than the so called photomixing where one laser is kept fixed and another laser is temperature tuned to vary the mixing wavelengths. ARP uses a dendrimer based high power source pumped with two diode lasers where the beam is split into two arms: one arm remains stationary while the other arm scans the stationary beam that produces an interferogram, characteristic of the specimen-THz interaction. Up to 30 THz can be generated by ARP method with an average power of ~ 3-4 mW.

ARP’s TeraSpectra is a turn key spectrometer. Time domain measurements can be conducted over a time span of sub-Pico seconds to a few tens of Pico-seconds with a resolution of <100 fs. This wide range allows characterizing a number of molecular events important for biological and materials research. The spectrometer applications may be developed in diagnostics, pharmaceutical, and related areas. The main features ARP claims about this new spectrometer are:
• TeraSpectra is cost-effective with higher performance because of its next generation technology.
• A high power source enables probing of a wide variety of specimens thus expanding the scope of the spectrometer.
• High Signal to Noise Ratio (>2000).
• Room temperature operation
• High sensitivity: ~ 10 femtomol.

For more information, see ARP’s website or contact ARP by email: info@arphotonics.net.

“The real breakthrough in materials science is that for the first time you can use an electric field to close the bandgap and open the bandgap. No other material can do this, only bilayer graphene,” Wang said.

Because tuning the bandgap of bilayer graphene can turn it from a metal into a semiconductor, a single millimeter-square sheet of bilayer graphene could potentially hold millions of differently tuned electronic devices that can be reconfigured at will, he said.

Wang, post-doctoral fellow Yuanbo Zhang, graduate student Tsung-Ta Tang and their UC Berkeley and Lawrence Berkeley National Laboratory (LBNL) colleagues report their success in the June 11 issue of Nature.

“The fundamental difference between a metal and a semiconductor is this bandgap, which allows us to create semiconducting devices,” said coauthor Michael Crommie, UC Berkeley professor of physics. “The ability to simply put a material between two electrodes, apply an electric field and change the bandgap is a huge deal and a major advance in condensed matter physics, because it means that in a device configuration we can change the bandgap on the fly by sending an electrical signal to the material.”

The property that makes it a good conductor–its zero bandgap–also means that it’s always on. “To make any electronic device, like a transistor, you need to be able to turn it on or off,” Zhang said. “But in graphene, though you have high electron mobility and you can modulate the conductance, you can’t turn it off to make an effective transistor.”

While a single layer of graphene has a zero bandgap, two layers of graphene together theoretically should have a variable bandgap controlled by an electrical field, Wang said. Previous experiments on bilayer graphene, however, have failed to demonstrate the predicted bandgap structure, possibly because of impurities. Wang, Zhang, Tang and their colleagues decided to construct bilayer graphene with two voltage gates instead of one. When the gate electrodes were attached to the top and bottom of the bilayer and electrical connections (a source and drain) made at the edges of the bilayer sheets, the researchers were able to open up and tune a bandgap merely by varying the gating voltages.

The team also showed that it can change another critical property of graphene, its Fermi energy, that is, the maximum energy of occupied electron states, which controls the electron density in the material.

“With top and bottom gates on bilayer graphene, you can independently control the two most important parameters in a semiconductor: You can change the electronic structure to vary the bandgap continuously, and independently control electron doping by varying the Fermi level,” Wang said.

Because of charge impurities and defects in current devices, the graphene’s electronic properties do not reflect the intrinsic graphene properties. Instead, the researchers took advantage of the optical properties of bandgap materials: If you shine light of just the right color on the material, valence electrons will absorb the light and jump over the bandgap.

In the case of graphene, the maximum bandgap the researchers could produce was 250 milli-electron volts (meV). (In comparison, the semiconductors germanium and silicon have about 740 and 1,200 meV bandgaps, respectively.) Putting the bilayer graphene in a high intensity infrared beam produced by LBNL’s Advanced Light Source (ALS), the researchers saw absorption at the predicted bandgap energies, confirming its tunability.
Because the zero to 250 meV bandgap range allows graphene to be tuned continuously from a metal to a semiconductor, the researchers foresee turning a single sheet of bilayer graphene into a dynamic integrated electronic device with millions of gates deposited on the top and bottom.

“All you need is just a bunch of gates at all positions, and you can change any location to be either a metal or a semiconductor, that is, either a lead to conduct electrons or a transistor,” Zhang said. “So basically, you don’t fabricate any circuit to begin with, and then by applying gate voltages, you can achieve any circuit you want. This gives you extreme flexibility.”

“That would be the dream in the future,” Wang said. Depending on the lithography technique used, the size of each gate could be much smaller than one micron, allowing millions of separate electronic devices on a millimeter-square piece of bilayer graphene.

Wang and Zhang also foresee optical applications, because the zero-250 meV bandgap means graphene LEDs would emit frequencies anywhere in the far- to mid-infrared range. Ultimately, it could even be used for lasing materials generating light at frequencies from the terahertz to the infrared.

“It is very difficult to find materials that generate light in the infrared, not to mention a tunable light source,” Wang said.

Crommie noted, too, that solid state physicists will have a field day studying the unusual properties of bilayer graphene. For one thing, electrons in monolayer graphene appear to behave as if they have no mass and move like particles of light–photons. In tunable bilayer graphene, the electrons suddenly act as if they have masses that vary with the bandgap.

“This is not just a technological advance, it also opens the door to some really new and potentially interesting physics,” Crommie said.

For more information see the paper, Direct observation of a widely tunable bandgap in bilayer graphene, in Nature.

Source: Laser Focus World.

EEs from the University of California at San Diego (UCSD) presented their design at the IEEE RFIC Symposium in Boston on June 9. The chip operates in the terahertz range (1 THz = 1,000 GHz) to provide X-ray-like vision, but using safe, naturally occurring millimeter wavelengths. The designers said the chip could be produced using inexpensive silicon processing techniques.

“Our chip can resolve images down to a millimeter scale, enabling us to identify very small objects that are on someone’s body,” said professor Gabriel Rebeiz, a designer of millimeter-wave RFICs, phased arrays and microelectromechanical system (MEMS) chips, in whose UCSD lab the SiGe terahertz RFICs were built.

In addition to their envisioned use for security applications, terahertz imagers could aid in navigation when storm or dust-cloud conditions limit visibility, as well as transfer enormous amounts of data over secure line-of-sight connections.

Because silicon-based semiconductors do not ordinarily operate above 10 GHz, imager designers today use expensive gallium arsenide or indium phosphide amplifiers. At the RFIC Symposium, however, several designs using CMOS and BiCMOS processes were described in addition to UCSD’s SiGe solution, promising less costly processes that could be run on standard silicon fabrication equipment.

“We should be able to bring the costs of those sorts of systems down, perhaps even to handheld scanners,” said Jason May, an EE doctoral candidate who works at Rebeiz’ UCSD lab.

The lab’s terahertz imager prototype implemented a W-band square-law detector in a commercial SiGe process and included an integrated low-noise amplifier and switch on a chip that consumed just 0.26 square millimeters. The chip operated at 94 GHz consuming 29 milliamps from a 1.2-volt supply.

Source: EETimes.com.

Scientists at The Univ. of Nottingham, in collaboration with colleagues in the Ukraine, have produced a new type of acoustic laser device called a Saser. It’s a sonic equivalent to the laser and produces an intense beam of uniform sound waves on a nano scale. The new device could have significant and useful applications in the worlds of computing, imaging, and even anti-terrorist security screening.

Where a “laser” (light amplification by the stimulated emission of radiation), uses packets of electromagnetic vibrations called “photons”, the “Saser” uses sound waves composed of sonic vibrations called “phonons”. In a laser, the photon beam is produced by stimulating electrons with an external power source so they release energy when they collide with other photons in a highly reflective optical cavity. This produces a coherent and controllable shining beam of laser light in which all the photons have the same frequency and rate of oscillation. From supermarket scanners to DVD players, surgery, manufacturing, and the defense industry, the application of laser technology is widespread.

The Saser mimics this technology but using sound, to produce a sonic beam of “phonons”’ which travels, not through an optical cavity like a laser, but through a tiny manmade structure called a “superlattice”. This is made out of around 50 super-thin sheets of two alternating semiconductor materials, gallium arsenide and aluminium arsenide, each layer just a few atoms thick. When stimulated by a power source (a light beam), the phonons multiply, bouncing back and forth between the layers of the lattice, until they escape out of the structure in the form of an ultra-high frequency phonon beam.

A key factor in this new science is that the Saser is the first device to emit sound waves in the terahertz frequency range…the beam of coherent acoustic waves it produces has nanometer wavelengths (billionths of a meter). Crucially the ‘superlattice’ device can be used to generate, manipulate and detect these soundwaves making the Saser capable of widespread scientific and technological applications. One example of its potential is as a sonogram, to look for defects in nanometer scale objects like micro-electric circuits. Another idea is to convert the Saser beam to THz electromagnetic waves, which may be used for medical imaging and security screening. High intensity sound waves can also change the electronic properties of nanostructures so a Saser could be used as a high-speed terahertz clock to make the computers of the future a thousand times faster.

Professor Anthony Kent from the University’s School of Physics and Astronomy, says “While our work on sasers is driven mostly by pure scientific curiosity, we feel that the technology has the potential to transform the area of acoustics, much as the laser has transformed optics in the 50 years since its invention.”

The research team at Nottingham, with help from Borys Glavin of the Lashkarev Institute of Semiconductor Physics in the Ukraine, has won the immediate accolade of the publication of their paper on the Saser experiments in this month’s Physical Review. The team has also won a grant of £636,000 from the Engineering and Physical Sciences Research Council to develop Saser technology over the next four years.

Source: R&D Magazine and University of Nottingham.

The Frenchman Jannick Chassagneux works as a PhD Student at the Institut d’Electronique Fondamentale (IEF) of the Université Paris Sud in France. His innovative R&D paper in photonics is entitled: “THz quantum cascade lasers with ultimate control of mode pattern and divergence”. The award committee appreciated Chassagneux’s work as “outstanding and excellent” as his research activity fully met the expectations of the Photonics21 Student Innovation Award.

During his undergraduate work, Chassagneux worked on a theoretical proposal for a new generation of mid-infrared optoelectronic devices operating in the strong-coupling regime between light and matter. In his PhD period, Chassagneux focused on the physics and technology of THz semiconductors laser sources with an emphasis on the development of innovative solutions based on photonic crystal technology. He carried out original theoretical and experimental work and published 9 articles in high-level, internationally refereed journals and gave several presentations at international conferences. The culmination of Chasagneux’s research activity has been the demonstration of a novel, highly effective photonic technology to control the spectral and spatial output properties of THz semiconductor lasers. The result, published in the journal Nature, will also have an impact on applications.

The award committee was set up of nine European photonics experts who are members of the 7 Photonics21 work groups. It has been elected for a term of 3 years.

By the closing date on the 31 st of March 2009, 44 applications were submitted, which can be regarded as a great success. Due to several excellent works, the selection committee evaluated the decision for one winner as very difficult and nominated two runners-up. Andreas Jechow from the University of Potsdam in Germany was placed second. He worked on the topic “Tailored light from external cavity enhanced broad area diode lasers – enabling new applications”. James Stone from the University of Bath in the United Kingdom handed in an excellent paper on “Blue-to ultraviolet-enhanced optical supercontinuum sources” and was placed third. Both received an official certificate during the award ceremony.

The Photonics21 Student Innovation Award has been established in order to promote research in photonics especially related to R&D with an industrial impact and to support and raise awareness for young European photonic researchers.

The next Photonics21 Student Innovation Award will be held in 2010.

Source: Nanowerk.com.

Commenting on the THz Electronics program, Dr. Mark Rosker, program manager of DARPA’s Microsystems Technology Office, said:

“The THz Electronics Program will develop a technology for integrated circuits operating at far higher frequencies than ever possible before. This will be crucially important for emerging applications like terahertz communications and radars. But of potentially even greater consequence, this program will drive the state of the art in high performance III-V electronics, with vast implication to RF circuits and systems operating at more conventional (microwave and millimeter-wave) frequencies.”

Contracts

So far, DARPA has awarded 4 contracts under the THz program. Note that “metrology” is the science of measurement.

May 6/09: Teledyne Scientific & Imaging in Thousand Oaks, CA received an $18.8 million cost-plus-fixed-fee contract to develop transceiver arrays; specifically, receivers and exciters at carrier frequencies of 670 GHz, 850 GHz, and 1030 GHz (HR0011-09-C-0060).

April 3/09: Northrop Grumman Aerospace Systems (formerly, Space and Mission Systems) in Los Angeles, CA received a $37 million contract for development of military and space satellites’ active receivers and transmitters operating at 670 gigahertz that ensure transmission of high-resolution images and other applications (HR0011-09-C-0062).

April 3/09: DARPA awards Northrop Grumman Electronic Systems an $8.9 million contract to develop and demonstrate technologies for high power amplification (HPA) of THz signals in compact HPA modules. These include demonstration of a power amplifier device capable of amplifying radiation at THz frequencies, the development of a compact THz HPA module (including an antenna and the ability to integrate with a solid-state exciter circuit), and THz metrology (HR0011-09-C-0061).

April 1/09: DARPA awards SAIC an $11.6 million contract to develop and demonstrate technologies for high power amplification (HPA) of THz signals in compact HPA modules. These include demonstration of a power amplifier device capable of amplifying radiation at THz frequencies, the development of a compact THz HPA module (including an antenna and the ability to integrate with a solid-state exciter circuit), and THz metrology (HR0011-09-C-0063).

Source: Defense Industry Daily

One highlight of the meeting is about Terahertz Modulators.

Scientists have for the first time devised a multi-pixel modulator for light waves at terahertz (THz, or 10^12 Hz) frequencies. The formal study of THz radiation, which can be described as far-infrared light, dates back many years, but has become increasingly widespread since around 1990, when efficient methods for generating and detecting the radiation become available. The expected applications include carrying out biological spectroscopy and imaging buried structures in semiconductors.

Rice University physicist Daniel Mittleman and his colleagues at Sandia and Los Alamos National Labs use a metamaterial to turn a stream of THz waves off and on. It’s called a metamaterial since it consists of an array of microscopic split metal rings. The rings can be controlled by nearby electrodes; modulating the ring’s capacitance, in turn, modulates the radiation; that is, the THz light (sometimes called T rays) can be switched so as to pass through or not. The modulator consists of 16 pixels in a 4 x 4 array. Mittleman reports that this is the first time the wavefront of a THz beam has been under electrical control, which is important because THz wavelengths may be good for imaging and this would be the first step in allowing that by sending light across a whole plane, not just as a linear burst. The switching speed, about 1 MHz, isn’t fast compared to today’s quickest data transmissions. But, Mittleman say, high bandwidth is not necessary for many of the imaging tasks that will be carried out by T rays. A larger 32 x 32 pixel array is now being designed.

Presentation CThX2; Thursday, June 4, 2:45 – 3 p.m.

Source: Business Wire.

Their destination is an area in space some 1.5 million kilometres further out from the Sun beyond the Earth. Known as Lagrange point L2, it is where a space probe can usefully hover, little disturbed by stray signals from home and without having to use much fuel to keep it in position.

First to arrive, in roughly two months’ time will be Planck – a microwave observatory like NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), which is also at L2. Planck will probe the geometry and contents of the universe by finely measuring the cosmic microwave background (CMB) radiation – a remnant of the Big Bang.

“Planck will provide a big jump in knowledge,” says Nazzareno Mandolesi of the Institute of Space Astrophysics and Cosmic Physics in Bologna, principal investigator for one of Planck’s two instruments, which will together measure the CMB at frequencies between 27 GHz to 1 THz.

More than a month later, Herschel, named after the German-born astronomer who in 1781 discovered Uranus, will join the group in a much wider orbit around L2 than Planck. This far-infrared and submillimetre telescope will study the universe’s coolest objects, from the era when the first stars and galaxies were formed to the present day.

“Herschel is the first really big infrared telescope,” says astrophysicist Michael Rowan-Robinson of Imperial College London. “For the first time we will get a proper sense of star formation in [other] galaxies.”

Cosmic echo
The Planck mission has a more focused goal than Herschel: to map out the CMB in the finest detail yet. The CMB was created 400,000 years after the Big Bang, when primordial protons, neutrons and electrons formed neutral atoms that allowed photons to finally move freely. The photons have continued to do so ever since, being stretched to microwave frequencies due to the expansion of the universe.

The European Space NASA’s Cosmic Background Explorer (COBE) set the field alight in 1992 when it revealed that the CMB is not uniform but has slight variations that carry information about the early universe.

“It transformed the field completely,” says astrophysicist Pedro Ferreira of the University of Oxford. Researchers set to work on a raft of new instruments, ground-based, airborne and in orbit, including WMAP and Planck.

The value of Planck and other CMB experiments is that they provide some of the only hard data about the very early universe. Cosmologists believe that the nascent universe underwent a period of extremely rapid growth called inflation and Ferreira says that Planck will be able to “distinguish between different theories of inflation and decide what theories are actually viable”.

The Degree Angular Scale Interferometer, sited at the South Pole, found the first evidence that the CMB photons are polarized; and Planck will measure that polarization in more detail than was possible before.

The big challenge for Planck will be to detect a so far unobserved type of polarization known as “B-modes”, which date back to the period of inflation and are determined by the density of primordial gravitational waves.

“This is a signal that has gone unobstructed since the Big Bang,” says Ferreira. If they could be detected, thinks Ferreira, such waves might tell us what mechanism generated them in the universe’s first moments, what caused inflation, and even if there was something before the Big Bang.

Eye in the sky
Herschel has two goals: to study star formation in our galaxy; and galaxy formation across the universe. It is hard to see star-forming regions at visible wavelengths because they are usually shrouded in gas and dust that block visible light. Infrared light pierces this veil and Herschel has the resolution to reveal the details of how clouds of cool atoms and molecules coalesce into stars.

As water vapour in the atmosphere absorbs much of the infrared radiation from space, astronomers have long been trying to get telescopes above the atmosphere. IRAS, a US- UK-Netherlands mission in 1983, was the first to map the entire sky, followed by ESA’s Infrared Space Observatory (ISO) in the 1990s and NASA’s current Spitzer Space Telescope.

Source: Physics World.

By modifying a commonly used commercial infrared spectrometer to allow operation at long-wave terahertz frequencies, the researchers discovered an efficient new approach to measure key structural properties of nanoscale metal-oxide films used in high-speed integrated circuits.

Chip manufacturers deposit complicated mazes of layered metallic conductor and semiconductor films interlaced with insulating metal oxide nanofilms to form transistors and conduct heat. Because high electrical leakage and excess heat can cause nanoscale devices to operate inefficiently or fail, manufacturers need to know the dielectric and mechanical properties of these nanofilms to predict how well they will perform in smaller, faster devices.

Manufacturers typically assay the structure of metal oxide films using x-ray spectroscopy and atomic force microscopy, both tedious and time-consuming processes. NIST researchers discovered that they could extract comparable levels of detail about the structural characteristics of these thin films by measuring their absorption of terahertz radiation, which falls between the infrared and microwave spectral regions.

Although terahertz spectroscopy is known to be very sensitive to crystal and molecular structure, the degree to which the metal oxide films absorbed the terahertz light was a surprise to NIST researchers.

“No one thought nanometer-thick films could be detected at all using terahertz spectroscopy, and I expected that the radiation would pass right through them,” says Ted Heilweil, a NIST chemist and co-author of the paper. “Contrary to these expectations, the signals we observed were huge.”

The NIST team found that the atoms in the films they tested move in concert and absorb specific frequencies of terahertz radiation corresponding to those motions. From these absorbed frequencies the team was able to extrapolate detailed information about the crystalline and amorphous composition of the metal oxide films, replete with structures that could affect their function.

The team’s experiments showed that a 40-nm-thick hafnium oxide film grown at 581 k (307 °C) had an amorphous structure with crystalline regions spread throughout; nanofilms grown at lower temperatures, however, were consistently amorphous. According to Heilweil, an approximately 5-nm film thickness is the detection limit of the terahertz method, and the efficacy of the technique depends to some degree on the type of metal oxide, though the group noted that all metal-oxide materials surveyed exhibit distinct spectral characteristics.

Source: Photonics.com and www.nist.gov.

Work is to be performed in Thousand Oaks, Calif. (69.84%), Santa Barbara, Calif. (12.8%), Tewksbury, Mass. (1.36%), La Jolla, Calif. (3.02%), and Pasadena, Calif. (13.70%) with an estimated completion date of Apr. 30, 2011.

Unlimited bids were solicited with 9 bids received.

But a series of experiments at the London Centre for Nanotechnology (LCN), led by Dr Paul Warburton and Dr Jon Fenton, centred around a new generation of devices only nanometres in size, are working towards producing data with enormous consequences.

This strange coupling of the massive with the minuscule is a consequence of speculation that the vacuum of space is not quite as empty as we would believe. Instead it is bristling with zero-point fluctuations, a phenomenon predicted by quantum mechanics, the area of physics modified to account for the unusual behaviour of matter on the small scale. The Heisenberg uncertainty principle, well known for the assertion that it is impossible to know both a particle’s position and momentum at the same instant,. It also demands that even the vacuum of space must possess some form of residual energy. Due to the assertion of equality between energy and mass, this vacuum energy is believed to take the form of ‘virtual particles’ continually popping in and out of existence.

Suggestions that this vacuum energy is in fact the enigmatic substance referred to perplexingly as ‘dark energy’ have caused quite a stir. Dark energy, one of the unsolved mysteries of modern cosmology, is believed to make up over 75% of the universe and be responsible for the acceleration of the universe’s expansion. It is proving difficult to define; there have been many theories put forward to describe dark energy – quintessence, phantom fields, chaotic scalar fields to name a few – all rather unfamiliar concepts and all as of yet unsubstantiated. As an explanation zero-point energy is appealing in its reassigning new meaning to a concept that has already been around for decades and is well grounded in other theory.

While the physical basis behind this theory of dark energy is phrased in a language we understand, the experimental difficulties Drs Warburton and Fenton encounter in the course of their work are substantial. They use devices that may hold some answers, devices based on Josephson junctions. The Josephson junctions themselves are tiny electronic devices consisting of strips of superconducting material, in which a current experiences no resistance, and separated by a thin insulating gap. In such a setup it is another consequence of the Heisenberg uncertainty principle that there is a probability for the electron to be present in the insulating layer and, under the right circumstances, it can effectively ‘tunnel’ across the insulating gap, resulting in the flow of a current.

As in any electronic set-up the effects of background noise must be taken into account, but whereas in most experiments noise is a nuisance to be minimised as far as possible, in these investigations one component in the spectrum of noise is the area of real interest.

At low temperatures, when the thermal excitations in the superconducting material are somewhat suppressed, the current due to noise is dominated by zero-point fluctuations. The potential for proof, or at least compelling evidence, as to whether vacuum energy is in fact dark energy lies in a limit placed on the vacuum energy by astronomical observations of the amount of dark energy in the universe. The finite value of dark energy density dictates that the team should see no zero-point fluctuation current generated above a critical frequency of around 1.7 THz.

The biggest challenge now is to develop experimental equipment capable of measuring the background noise up to such high frequencies. By exploring the properties of high-temperature superconductors the team at the London Centre for Nanotechnology, in collaboration with scientists at the University of Cambridge, hope to take measurements across the critical THz frequency range.

The implications of verifying the upper limit and connecting vacuum energy with dark energy would be huge, throwing light onto the formation of the current universe and fuelling predictions for its future. But in the atmosphere of uncertainty and even controversy surrounding the theory any answers either way to the question of whether we can measure dark energy in a laboratory will be a welcome step in moving towards long searched for answers.

Source: Nanowerk News

At the Terahertz Sensing and Imaging Laboratory at RIKEN (Aramaki, Japan), a prototype apparatus has been built to inspect all mail handled in Japanese international post offices (around 100,000 items per day). However, the THz spectrometer takes too long to examine every package.

Therefore, to achieve complete inspection, the process has been divided into two stages. The first involves rapid screening using x-rays and THz waves, and the second identifies the suspicious substances selected in the first stage.

The initial screening stage uses x-rays to exclude envelopes containing only paper. Images revealing shadows are then scanned and measured at 0.54THz. For more information, go to: http://spie.org/x33690.xml?ArticleID=x33690

Source: Vision Systems

The deadline for applications is June 15, 2009.

For more information, see the Grants.gov call.

“This development will allow the many users of BWOs to upgrade their systems capabilities to 1.7 – 2.1 THz range. Output power of QS1-260-TT ranges from 1 to 5 ??W, which is well above sensitivity limit of good pyroelectric detectors and Golay Cells”, commented Dr. Hurlbut, senior research scientist at Microtech. “The extended spectral range, reduced footprint, lower operating voltage, and good reliability of the millimeter wave BWO’s make the hybrid electronic sources an excellent option for THz researchers and industrial applications specialists.”

This development is a result of a joint project between Microtech Instruments, Inc., Virginia Diodes, Inc., and Prof. Frank DeLucia of Ohio State University. The project was partly funded by DARPA SBIR program (topic number SB062-002), initiated by Dr. Henry Everitt.