A LASER-BEAM DEFLECTION TECHNIQUE FOR THE QUANTITATIVE DETECTION OF ULTRASONIC LAMB WAVES

Ultrasonic Lamb waves have been measured with a quantitative optical b eam deflection (OBD) technique. Calibration of the technique is derive d for two cases of laser probe beam cross-section, one with a uniform beam and the other with a Gaussian beam intensity distribution. Expres sions for angular beam deflection angle are derived for both cases in terms of the total light intensity falling on the photodetector, assum ed to have a square-law voltage response. Using a Gaussian beam intens ity distribution from a HeNe laser, the OBD measurements were compared with those from a Michelson interferometer to show that measurements were self-consistent.