ABSTRACT
The ambient atmosphere has an effect on the laser-induced damage threshold mainly because of induced absorption. It must be realized that even ‘cleaning’ can add absorption, as well as reducing it. Laser-induced gas breakdown consists of three steps, preionization, ionization growth and absorption. Ionization growth occurs by impact ionization and can proceed only once an initial charge is supplied. The number of initial electrons will grow exponentially at a rate which is linearly dependent on the intensity and the ionization potential and inversely dependent on the pressure and the pulse duration. The statistical distribution of breakdown times of gas volumes irradiated with square waveform pulses has been shown to account for the probability that initial electrons are produced by photoionization. Continuous wave laser-induced damage in semiconductors has been concluded to be dominated by parametric instability in solid-state plasmas. In the infrared, photodetectors frequently employ semiconducting windows or lenses in front of the detector surface.
