Acoustic emission during laser annealing of silicon single crystals

The acoustic response of silicon single crystals to the action of a millisecond laser pulse, with an excitation wavelength 1.06 μm, has been investigated. It has been discovered for the first time that additional acoustic emission, delayed in time with respect to the photoacoustic response, is observed for laser energy flux density above the threshold corresponding to surface melting. The delay time depends linearly on the laser radiation power and varies from one to tens of milliseconds. It is shown, by comparing the parameters of the acoustic emission with the dynamical development of thermoelastic stresses in the laser action zone as well as with the kinetics of melting of the irradiated surface, that crack formation under the action of the thermoelastic stresses is the source of the additional acoustic emission. Fiz. Tverd. Tela (St. Petersburg) 39, 505–509 (March 1997)