Transmission of intense femtosecond laser pulses into dielectrics.

The interaction of intense, femtosecond laser pulses with a dielectric medium is examined using a numerical simulation. The simulation uses the one-dimensional electromagnetic wave equation to model laser pulse propagation. In addition, it includes multiphoton ionization, electron attachment, Ohmic heating of free electrons, and temperature-dependent collisional ionization. Laser pulses considered in this study are characterized by peak intensities approximately 10(12) -10(14) W/cm(2) and pulse durations approximately 10-100 fsec . These laser pulses interacting with fused silica are shown to produce above-critical plasma densities and electron energy densities sufficient to attain experimentally measured damage thresholds. Significant transmission of laser energy is observed even in cases where the peak plasma density is above the critical density for reflection. A damage fluence based on absorbed laser energy is calculated for various pulse durations. The calculated damage fluence threshold is found to be consistent with recent experimental results.