A model for wide bandgap materials was developed to study the breakdown behavior under multiple subpicosecond laser pulse illumination. While this model has been applied to the study oxide materials, it is general enough to be used with any wide bandgap material. The model distinguishes two types of midgap trapping states - shallow and deep traps (defects), which can be native or laser induced. Excitation of these midgap states enhances the seed for the avalanche ionization process that causes breakdown, lowering the damage fluence for pulses later in the train. A set of rate equations for the conduction band electron density and population dynamics of the trap states was solved numerically to predict the damage threshold as a function of pulse number F(M). The effect of trap level parameters such as density, absorption cross-section, and the initial population on the shape of F(M) is discussed. Comparison is made to experimental data for oxide thin films.

Date Published: 30 December 2008
PDF: 10 pages
Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 713209 (30 December 2008); doi: 10.1117/12.804430

Published in SPIE Proceedings Vol. 7132:
Laser-Induced Damage in Optical Materials: 2008
Gregory J. Exarhos; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)