Size effect and statistics of laser damage to alkali-halide crystals at the 10.6 μ wavelength

An investigation was made of the size dependence of the thresholds for laser damage to NaCl and KCl crystals at the 10.6 μ wavelength. It was found that this was due to spatial fluctuations of the optical density. A statistical theory of laser damage in focused beams is developed. The resultant dependence of the threshold on the size of the focal region is compared with the experimental data. It is found that under sharp focusing conditions, the damage thresholds may exceed the threshold for avalanche ionization as a result of the absence of initiating electrons.