An ultrasonic analog for a laser

Abstract

We report measurements on two simple ultrasonic systems analogous to random lasers. One system entails unstable ultrasonic feedback between distinct piezoelectric transducers on an irregularly shaped high-Q solid; another involves a spontaneously emitting piezoelectric device that can also emit by stimulation. Both are found to exhibit some of the behaviors of lasers. Over a wide range of parameters we observe narrow single-emission lines (natural width is estimated at about 0.000<th>000<th>000<th>1 Hz), sensitivity to linear cavity properties, complex multimode emissions, and line narrowing.