This year marks the 50th anniversary of the invention of the laser, which now has an extraordinarily diverse and growing range of applications, from consumer electronics to the highest-precision metrology. Two independent studies using quite different approaches now report successful coherent sound wave amplification, in which mechanical vibrations are produced by processes that mimic stimulated light emission in laser operation. Grudinin et al. use a coupled optomechanical resonator system in which excitation by an optical laser induces mechanical oscillations. Above a critical threshold power of the pump laser, amplification and gain of the mechanical oscillations are observed, producing coherent sound from radio to microwave frequencies. Beardsley et al. use a superlattice semiconductor system to which an electric field is applied. Precise tuning of the superlattice structure produces coherent sound at several hundred GHz, in range of the clothes-penetrating THz scanners being rolled out at airports. The ability to produce intense and coherent beams of sound in these frequency ranges should find immediate application in the imaging technology sector.
Phys. Rev. Lett. 104, 83901; 85501 (2010).
