A laser beam deflection technique for the quantitative detection of ultrasonic Lamb waves

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