Features of Femtosecond Laser Ablation of Porous Silicon Layers in an Aqueous Medium

We report an experimental investigation of the ablation thresholds of porous and single-crystal silicon in water and air under femtosecond laser irradiation (pulse energy, 1–10 μJ; wavelength, 1032 nm; pulse duration, 270 fs; pulse repetition rate, 100 kHz; and focal spot size, 50 μm). The presence of an aqueous medium decreases the laser ablation threshold. It is shown that the ablation threshold decreases with increasing sample porosity. The sample morphology is studied, revealing various surface modifications depending on the laser pulse energy and the surrounding medium.