LASER INTERFERENCE GRATING FOR SURFACE WAVE GENERATION

Abstract

An optical method for generating and detecting periodic surface acoustic waves is described. The periodic source is created by splitting the beam from a Nd:YAG laser and recombining the beams at a sample surface to form an interference pattern. The periodic surface waves launched from the source are detected optically using either a modified Michelson interferometer or by laser probe beam deflection. In both cases the detection spot is smaller than the ultrasonic wavelength. Rayleigh waves in the 1–20 MHz frequency range can readily be generated and detected on thick aluminium samples (plate thickness greater than the wavelength). It is also possible to generate narrowband Lamb waves in plates which are thin compared to the wavelength, experimental and theoretical waveforms are presented for this case.

KEY WORDS:

• Laser ultrasound
• periodic surface waves

Additional information

Notes on contributors

H. NAKANO

on leave from National Research Laboratory of Metrology, 1-1-4. Umezono, Tsukuba-shi, Ibaraki, Japan