Laser-induced breakdown by impact ionization in SiO2 with pulse widths from 7 ns to 150 fs

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Abstract
Results of laser‐induced breakdown experiments in fused silica (SiO2) employing 150 fs–7 ns, 780 nm laser pulses are reported. The avalancheionization mechanism is found to dominate over the entire pulse‐width range. Fluence breakdown threshold does not follow the scaling of F th∼ √τ p , when pulses are shorter than 10 ps. The impactionization coefficient of SiO2 is measured up to ∼3×108 V/cm. The relative role of photoionization in breakdown for ultrashort pulses is discussed.