Laser‐Beam‐Induced Ultrasonic Waves in Glass

Ultrasonic waves have been produced in samples of various glasses by passing a Q‐spoiled laser beam through the sample. The ultrasonic waves were observed at a frequency arbitrarily chosen as 266 kc/sec, but in general they consist of a broad spectrum. Various theoretical explanations have been explored, and the most palusible one has been found to be that of Chiao, Townes, and Stoicheff [Phys. Rev. Letters 12, 592 (1964)] and Garmire, Pandarese, and Townes [ibid. 11, 160 (1963)], originally formulated to explain the production of hypersonic waves through electrostriction at larger energy densities. The theoretical prediction is that the effect should grow linearly with the laser‐beam intensity and increase very rapidly with the index of refraction.