Laser-generated ultrasonic beams

A device has been developed which uses a Q‐switched laser pulse to produce a plane compressive stress pulse or a slowly decaying sinusoidal stress wave train in any solid or liquid material. The device utilizes a thin liquid layer to totally absorb the laser pulse and generate a stress pulse by rapid thermal expansion. Compressive stress pulses of 200 nsec duration and up to 5 kilobar amplitude have been obtained. Wave trains of about 30 cycles duration and 1/4 kilobar amplitude (peak‐to‐peak in typical solids) have been obtained at frequencies between 1–25 MHz. Stress amplitudes may be varied by filtering the incident laser radiation. The laser radiation does not damage this transducer, so it may be used indefinitely.