THE DETECTION OF EXTREMELY SMALL MECHANICAL DISPLACEMENTS GENERATED BY A DE-FOCUSED LASER-BEAM

Low-amplitude ultrasonic signals are generated by a pulsed laser and d etected either by optical techniques or by conventional piezoelectric transducers. A one-dimensional model of laser-induced displacements of the sample back surface is explained, taking into account the bulk ab sorption of laser light. Experimental confirmation of the model was at tained. Excimer-laser-induced waves were detected by a stabilized Mich elson interferometer and simultaneously by a piezoelectric transducer. By extrapolating the calibration, it is shown that displacements of o rder 10(-14) m are generated with low-intensity laser pulses via a the rmoelastic mechanism and that these can be detected by using a piezoel ectric transducer.