Laser generation of ultrasound using a modulated continuous wave laser diode

A modulated continuous wave diode laser was used to generate ultrasonic Lamb waves in a thin steel plate. No surface damage was evident on the sample, a feature due to the low power density of the acoustic source in contrast to the high power pulsed laser systems usually employed for laser-ultrasound generation. The Lamb waves were monitored using a surface bonded optical fiber interferometer whose output was correlated with the pseudorandom binary sequence used to modulate the laser diode. In this fashion, it was possible to record a time domain history of the ultrasonic propagation in the sample. (C) 1998 American Institute of Physics.