Hypersound
Hypersound, acoustic pulsation at 200 gigahertz frequencies, has been produced in the same kind of resonant multilayered semiconductor cavity as used in photonics. Physicists at the Institute des Nanosciences de Paris and the Centro Atomico Bariloche and Instituto Balseiro, in Argentina, generate the high frequency sound pulses in a solid material made of thin gallium-arsenide and aluminum-arsenide layers. One can picture the sound, excited by a femtosecond laser, as being a short pulse of waves or equivalently as particle-like phonons, excitations pulsing through the stack of layers. These phonons are reflected at either end of the device, called a nanocavity, by further layers with a much different acoustic impedance acting as mirrors. Acoustic impedance is the acoustic analog of the refractive index for light.
Bernard Jusserand (bernard.jusserand@insp.jussieu.fr, 33-1-4427-6980) says that he and his colleagues hope to reach the terahertz acoustic range. The wavelength for such “sound” is only nanometers in length. They believe that a new field, nanophononics, has been inaugurated, and that the acoustical properties of semiconductor nanodevices will become more prominent. Terahertz phonons, and more specifically the reported nanocavities could, for example, be used to modulate the flow of charges or light at high frequency and in small spaces. Terahertz sound might also participate in the development of powerful “acoustic lasers” or in novel forms of tomography for imaging the interior of opaque solids.
Huynh et al., Physical Review Letters, 15 September 2006
Contact Bernard Jusserand
Institut des Nanosciences de Paris
bernard.jusserand@insp.jussieu.fr, +33-1-4427-6980
Source: Physics News Update.