Ultrafast laser-induced modifications of energy bands of non-metal crystals

Vitaly Gruzdev

doi:10.1117/12.836908

31 December 2009 Ultrafast laser-induced modifications of energy bands of non-metal crystals

Vitaly Gruzdev

Proceedings Volume 7504, Laser-Induced Damage in Optical Materials: 2009; 75040G (2009) https://doi.org/10.1117/12.836908
Event: Laser Damage Symposium XLI: Annual Symposium on Optical Materials for High Power Lasers, 2009, Boulder, Colorado, United States

Abstract

Ultrafast laser-induced variations of electron energy bands of transparent solids significantly influence ionization and conduction-band electron absorption driving the initial stage of laser-induced damage (LID). The mechanisms of the variations are attributed to changing electron functions from bonding to anti-bonding configuration via laser-induced ionization; laser-driven electron oscillations in quasi-momentum space; and direct distortion of the inter-atomic potential by electric field of laser radiation. The ionization results in the band-structure modification via accumulation of broken chemical bonds between atoms and provides significant contribution to the overall modification only when enough excited electrons are accumulated in the conduction band. The oscillations are associated with modification of electron energy by pondermotive potential of the oscillations. The direct action of radiation's electric field leads to specific high-frequency Franz-Keldysh effect (FKE) spreading the allowed electron states into the bands of forbidden energy. Those processes determine the effective band gap that is a laser-driven energy gap between the modified electron energy bands. Among those mechanisms, the latter two provide reversible band-structure modification that takes place from the beginning of the ionization and are, therefore, of special interest due to their strong influence on the initial stage of the ionization. The pondermotive potential results either in monotonous increase or oscillatory variations of the effective band gap that has been taken into account in some ionization models. The classical FKE provides decrease of the band gap. We analyzing the competition between those two opposite trends of the effective-band-gap variations and discuss applications of those effects for considerations of the laser-induced damage and its threshold in transparent solids.

Citation Download Citation

Vitaly Gruzdev "Ultrafast laser-induced modifications of energy bands of non-metal crystals", Proc. SPIE 7504, Laser-Induced Damage in Optical Materials: 2009, 75040G (31 December 2009); https://doi.org/10.1117/12.836908

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