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7 June 2006 Free-electron generation in laser-irradiated dielectrics
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Proceedings Volume 6261, High-Power Laser Ablation VI; 62610S (2006)
Event: High-Power Laser Ablation 2006, 2006, Taos, NM, United States
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.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
B. Rethfeld "Free-electron generation in laser-irradiated dielectrics", Proc. SPIE 6261, High-Power Laser Ablation VI, 62610S (7 June 2006);

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