Damage Threshold Studies in Laser Crystals: Experimental and Theoretical Results in Ruby and Sapphire

Abstract

Abstract : The results of a number of experiments are presented as well as a summary of the theoretical work. Bulk damage thresholds for several ruby and sapphire samples from different sources are presented. The problem of surface damage is discussed, and qualitative comparisons between entrance and exit surface damage are made. Differences between the gross characteristics of bulk damage in ruby and sapphire are presented and discussed. The dependence of damage threshold on TiO2 doping and optical pumping is presented. The theoretical treatment deals with processes by which 'cold' conduction electrons may damage the lattice before they gain enough energy to ionize their surroundings. It is shown that the energy that the conduction electrons absorb linearly from the optical beam is deposited almost immediately in the lattice and is of sufficient magnitude to form a rupturing shock wave. It is also shown that the photoexcitation of impurity levels is enhanced by the presence of conduction electrons. The presence of conduction electrons and excited impurities is likely to alter the refractive index significantly and affect the focusing (self or external) in a complicated way. Implications of these results for raising damage thresholds are discussed.