Determination of the characteristics of microdefects from statistical relationships governing laser damage to solid transparent materials

An investigation was made of the nature of the dependence of the bulk laser damage threshold of solid transparent materials on the size of the focusing-lens caustic. Experiments carried out on a large number of different samples of NaCl and KCl crystals showed that for $\lambda$ = 10.6 $\mu$ and the focusing-lens caustic diameter $\gtrsim$ 23 $\mu$, the dependence on this diameter was due to the presence of microdefects. It was also established that in the case of $\lambda$ = 1.06 $\mu$ radiation and small caustics (5–30 $\mu$) the same dependence could be unrelated to microdefects. A statistical theory was developed for determining the distribution function of the defect damage thresholds from the nature of the size dependence.