Ultrafast electron dynamics in femtosecond laser dielectric breakdown

We investigate the laser damage mechanism in optical materials. We present the first single-shot damage threshold measurement in fused silica as a function of pulse duration down to 20 fs. Dielectric breakdown is explained in terms of free electron generation initiated by the laser pulse. We develop a model using the rate equation for the density of conduction electrons to calculate the damage threshold at different pulse widths. More complete and realistic models for photoionization and impact ionization are applied in the rate equation. Previously observed conflicting results of the dependence of damage threshold on pulse duration can be explained by our model. The model shows that in the short pulse regime, the damage threshold is sensitive to the initial conduction electron density. Front-surface damage, instead of backside damage, for short pulses in a thin fused-silica plate was observed for the first time in our laboratory. For some pulse durations, the damage occurred on both sides of the sample. We found that the damage location depends on pulse duration and polarization.; Applications of laser-induced breakdown are discussed. We improve the dynamic range of a streak camera by employing the plasma shuttering effect associated with laser-induced breakdown. Plasma shuttering causes reduction in transmission of the peak of the laser pulse, and can be served as a protection device for sensitive detectors. A dynamic range of 107 with possible extension to 109 of pulse contrast measurement over a nanosecond range with a picosecond resolution is demonstrated. Sub-spot size deposition features can be achieved by use of short-pulse lasers because of the deterministic threshold and the high nonlinearity of laser damage for short pulses. We demonstrate aluminum deposition of a 0.8-μm diameter. The dynamics of the short-pulse metal deposition process is proposed.; In addition, laser development work in the preparation of laser-induced damage study is presented. A kilohertz chirped-pulse amplification regenerative laser system is described. A technique of intracavity spectral shaping with birefringence is devised to broaden the bandwidth of a laser system. The errors due to geometries in pulse measurement due to geometries are analyzed.