Theory analysis of wavelength dependence of laser-induced phase explosion of silicon

Wavelength dependence of laser ablation of silicon was investigated with nanosecond ultraviolet, visible, and infrared laser pulses in the irradiance range from 3×10¹⁰ to 1×10¹² W/cm². For 266 and 532 nm laser pulses, the depth of laser-produced crater shows a dramatic increase at a laser irradiance threshold of approximately 2×10¹⁰ to 4×10¹¹ W/cm² respectively, above which, large micron-sized particulates were observed to eject from the target about 300–400 ns after the laser pulse. In contrast, for 1064 nm pulse, this dramatic increase was not observed. The underlying mechanism for the observed threshold phenomenon is presented in this study, which can be attributed to the thermal diffusion and subsequent explosive boiling after the completion of the interaction between the nanosecond laser pulse and silicon. Based on our delayed phase explosive model, the ablation depths were calculated for different wavelengths and compared to experimental results. Plasma shielding during laser irradiation was included in the model, which plays a key role to the coupling of laser energy to the irradiated material.