Plume shielding effects in ultrafast laser surface texturing of silicon at high repetition rate in air

We analyze surface texturing induced by femtosecond laser irradiation of a silicon target at high repetition rates. The features of the produced surface structures in ablative conditions, i.e. at fluences larger than the ablation threshold, are investigated as a function of number of pulses and pulse energy, for various repetition rates, in the range 10 Hz-200 kHz. Our experimental findings highlight a significant influence of the pulse repetition rate on both surface texture and crater size produced by irradiation with a fixed sequence of N laser pulses. This effect is ascribed to plume shielding occurring at repetition rates larger than approximate to 10 kHz.