Investigation of mechanisms of damage induced in ionic crystals by pulsed nanosecond laser radiation

The laser-induced damage of ionic crystals (primarily alkali metal halides) was investigated in a wide range of wavelengths (0.53-10.6 microns) in order to clarify the role of avalanche ionization in the damage. YAG:Nd(3+) (0.53 micron), ruby (0.69 micron), and CO2 (10.6 microns) lasers were used in the investigation. It is found that the optical resistance of the crystals is enhanced by heat treatment. The frequency and temperature dependences of thresholds of laser damage are examined in detail, and conclusions are drawn concerning the damage mechanisms of ionic crystals. It is argued that, contrary to the results of previous studies, avalanche ionization does not play a predominant role in the laser-damage process.