Investigation of phase transition thresholds by nonlinear transient laser gratings on silicon surfaces

Abstract

Articles you may be interested inThe origins of pressure-induced phase transformations during the surface texturing of silicon using femtosecond laser irradiation Nonlinear transient laser gratings were excited by crossing two 180 ps Nd:YAG laser pulses ͑355 nm͒ at the silicon surface. The launched counterpropagating surface acoustic wave trains were detected outside the source with a cw laser probe-beam-deflection setup. Phase transitions occurring within the Gaussian fluence distribution of the grating induced characteristic changes in the amplitude of the corresponding grating oscillations involved and higher harmonics were found in the frequency spectrum. In the molten surface region, the amplitude decreased compared to the thermoelastic excitation, and second-harmonic generation was observed, whereas ablation generated an asymmetric profile with higher amplitudes and even the third harmonic could be detected. An accurate method is introduced to determine the ablation threshold ͑340 mJ/cm 2 for silicon͒ from the transition of linear to nonlinear behavior in the distorted non-Gaussian amplitude distribution.

In Situ Laser Synthesis of Si Nanowires in the Dynamic TEM

“…Its energy distribution is Gaussian, within a 2000 µm 2 spot size. The ablation thresholds reported by Gusev and co‐workers21, 22 for 355 nm laser treatments of Si were used as guidelines. Films of 〈111〉 Si with a 4 nm Au layer (as a catalyst) were treated with a frequency tripled (355 nm) Nd:YAG laser with 8 ns pulses at 200–275 µJ (for heating or ablation).…”