Damage induced on fused silica by fundamental frequency and third harmonic of Nd:YAG laser

The damage processes of fused silica under the fundamental frequency and third harmonic of Nd:YAG laser were studied with instantaneous scattering pulses measurements via fast photodiodes and high bandwidth oscilloscope. The optical micrographs of ablated craters on fused silica surface were also analyzed. The sharp increase of scattered light of pump pulse was assumed to be the damage precursor, therefore, the damage started nearly at the peak of the pump pulse. Fundamental frequency laser induced-damage of fused silica began before that of the third harmonic laser. The plasmas flash due to ion-electron recombination occurred about 21 ns after the peak of pump pulses. Based on Keldysh theory, the photoionization rate of fused silica vs laser intensity under 355 and 1 064 nm laser was calc