Abstract

A He-Ne laser-illuminated Mach-Zehnder interferometer has been used to study the time-resolved surface heating and deformation of various solid materials caused by irradiation with the second harmonic (530 nm) of a pulsed Nd: YAG laser. Both thin and thick metal and semiconductor samples have been studied. For thick samples the thermal stress caused by rapid absorption of laser energy leads to local surface expansion that produces a phase chirp of a He–Ne beam reflected from the deformed surface. For thin samples additional surface deformations result from stress-induced mechanical vibration of the sample. For thin samples the deformation of either the irradiated (front) surface or the back surface can be observed. Interferometric detection of the induced phase chirp, for small phase chirps, leads to a linearly related output signal. The signals for both thick and thin samples can be understood quantitatively on the basis of theories that include thermal expansion of the samples and classical resonant mechanical oscillation of two-edge-clamped thin plates. Quantitative measurements of both surface excursion and temperature rise have been made at laser energies substantially below the damage threshold. Extrapolation of our data yields a melting fluence for silicon of 0.42 J/cm².

© 1985 Optical Society of America