Detection of Laser Excited Surface Acoustic Waves by Infrared Radiation

Remote detection of ultrasonic waves is shown experimentally by measuring the infrared (IR) radation accompanying the adiabatic propagation of surface waves. The Rayleigh waves were excited by a pulsed Nd:yttrium-aluminum-garnet laser on the surface of a steel sample at temperatures up to 700 °C. The observed time-of-flight data of the Rayleigh waves correspond to values obtained by optical interferometry and the measured signal-to noise ratio of ~0.1 agrees with the estimated value using an IR detector with a sensitivity of D*=1.7X109mm/Hz/W. Further improvements of IR detection may lead to a viable tool for laser ultrasonics.