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29 November 2010 Femtosecond pulse S on 1 LIDT in dielectric materials: comparison of experiment and theory
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The multiple-pulse laser-induced breakdown behavior of dielectrics is modeled. The model is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations for the occupation and ionization of band and midgap states (native and laser induced). Using realistic estimations for the trap density and ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by avalanche ionization seeded by multiphoton ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the conduction band. The effect of native and laser-induced defects can be distinguished by their saturation behavior. The model explains the principal behavior of the LIDT of a pair of pulses as a function of the temporal separation. Using the model, the observed transients can be related to rate constants of electrons leaving the CB and midgap states.
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L. A. Emmert, M. Mero, D. N. Nguyen, W. Rudolph, D. Patel, E. Krous, and C. S. Menoni "Femtosecond pulse S on 1 LIDT in dielectric materials: comparison of experiment and theory", Proc. SPIE 7842, Laser-Induced Damage in Optical Materials: 2010, 784211 (29 November 2010);

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