SOUND-AMPLIFICATION BY STIMULATED-EMISSION OF PHONONS USING 2-LEVEL SYSTEMS IN GLASSES

We discuss different possibilities to amplify an ultrasonic wave in a glass by inverting the populations of the two-level systems: we show t hat the only convenient one is the so-called ''rapid adiabatic passage ''. We describe different steps of the procedure needed to apply it to a Tetrasil glass and the experimental results are presented. Emphasis is laid on the differences between our approach and Tucker's experime nt. Finally, the actual limitations are discussed and some means to ov ercome them are proposed.