Time-Resolved Reflectivity and Temperature Measurements During Laser Irradiation of Crystalline Silicon

Time-resolved reflectivity measurements have been used to characterize the temperature-dependence of the reflectivity of crystalline silicon between room temperature and the melting point during pulsed laser irradiation ([lambda] = 532 nm, pulse durations between 50 ns and 600 ns). Based on these measurements, the reflectivity [R.sub.Si]([T.sub.m]) of the hot solid just before the onset of melting was determined for the probe wavelength of [lambda] = 632.8 nm. For this wavelength, [R.sub.Si]([T.sub.m]) was found to be 39.8 % [+ or -] 0.6 %. The increase of the measured reflectivity was correlated to the laser-induced temperature increase of the silicon surface as calculated by solving the 1D heat-conduction equation. This approach allows to indirectly determine the temperature in the laser-material interaction zone on the surface of a silicon sample during pulsed laser irradiation with sub-nanosecond time resolution by monitoring its reflectivity. Keywords: reflectivity, silicon, laser, pump-probe, temperature dependence, melting point