On the mechanism of multi-pulses induced damage in dielectrics

The defects and color centers E′ in glass with laser flux F have been analyzed in terms of material damage threshold and the number of laser pulses. It is found that the multi-pulse induced damage can be grouped into four regions I, II, III and IV, depending on different laser-matter interactions under different laser pulse energies. Region I is characterized by the medium under high light intensity breakdown due mainly to nonlinear ionization; region II stands for the lower laser pulse energy of rapid defect accumulation, and medium damage can be viewed as the combination of non-linear ionization and accumulation of defects; region III is the break breakdown of dielectrics owing to the accumulation of defects and color centers under 355nm irradiation; the density of accumulated color center approaches steady state; region IV is an undamaged area where laser pulse energy is too low to engender defects in the dielectrics.