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Proceedings Paper

Free-electron generation in laser-irradiated dielectrics
Author(s): B. Rethfeld
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Paper Abstract

When transparent solids are irradiated with laser intensities above a certain threshold, strong absorption of laser energy occurs. The increasing absorptivity is caused by the formation of a free electron gas in the conduction band of the dielectric. The transient free electron density is a fundamental parameter for numerous theoretical and experimental investigations and applications. We study the mechanisms of free-electron generation in the frame of different approaches. A full kinetic treatment reveals a non-stationary behavior, which is neglected when applying the standard rate equation. A new model, the multiple rate equation, keeps track of the non-stationarity of the electron energy distribution while maintaining the conceptual and analytic simplicity of standard rate equation. We present the analytical asymptotic solution of the multiple rate equation which yields an expression for the avalanche coefficient and provides information about the validity of the standard rate equation. The numerical calculation shows the transient distribution of free electrons and the effect of the non-stationarity of its shape on the impact ionization probability. We study the role of different ionization processes and its dependence on laser pulse duration. The fraction of impact-ionized electrons is found to depend only on the product of pulse duration and intensity, i.e. on the fluence. A remarkable effect of the shape of the laserpulse on the total free electron density and the conditions for dielectric breakdown is found.

Paper Details

Date Published: 7 June 2006
PDF: 12 pages
Proc. SPIE 6261, High-Power Laser Ablation VI, 62610S (7 June 2006); doi: 10.1117/12.674623
Show Author Affiliations
B. Rethfeld, Gesellschaft für Schwerionenforschung mbH (Germany)

Published in SPIE Proceedings Vol. 6261:
High-Power Laser Ablation VI
Claude R. Phipps, Editor(s)

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