Modeling free-carrier absorption and avalanching by ultrashort laser pulses

Jeremy R. Gulley

doi:10.1117/12.899257

28 November 2011 Modeling free-carrier absorption and avalanching by ultrashort laser pulses

Jeremy R. Gulley

Proceedings Volume 8190, Laser-Induced Damage in Optical Materials: 2011; 819022 (2011) https://doi.org/10.1117/12.899257
Event: SPIE Laser Damage, 2011, Boulder, Colorado, United States

Abstract

In the past decade it was demonstrated experimentally that negatively-chirped laser pulses can lower the surface LIDT for wide band-gap materials by decreasing the number of photons required for photoionization on the leading edge of the pulse. Similarly, simulations have shown that positively-chirped pulses resulting from selffocusing and self-phase modulation in bulk dielectrics can alter the onset of laser-induced material modifications by increasing the number of photons required for photoionization on the leading edge of the pulse. However, the role of multi-chromatic effects in free-carrier absorption and avalanching has yet to be addressed. In this work a frequency-selective model of free-carrier dynamics is presented, based on a recently extended multi-rate equation for the distribution of electrons in the conduction band. In this model free-carriers gain energy from the field by single-photon absorption at the instantaneous frequency, which varies as a function of space and time. For cases of super-continuum generation it is shown that a Drude-type absorption can vary from 50% to over 200% the absorption rate as evaluated at the central pulse frequency only. Simulations applying this model to ultrafast laser-plasma interactions in fused silica explore how pulse chirps may be used as a distinguishing parameter for LID resulting from otherwise identical pulses.

Citation Download Citation

Jeremy R. Gulley "Modeling free-carrier absorption and avalanching by ultrashort laser pulses", Proc. SPIE 8190, Laser-Induced Damage in Optical Materials: 2011, 819022 (28 November 2011); https://doi.org/10.1117/12.899257

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