Structure impurity composition and laser damage threshold of the subsurface layers in KDP and KD*P single crystals

摘要

Abstract: The effect of the structure and degree of faultness of the subsurface layer which appears during the abrasive mechanical treatment of KDP and KD$+*$/P single crystals on the value of their surface laser damage threshold was studied in this paper. It was shown that flattening of the relief polycrystalline layer, decrease of the impurity (Ca, Al, Mg, c, etc.) concentration introduced by the abrasive and supplementary materials, used for the mechanical treatment of single crystals, as well as lowering the concentration of dislocations lead to a significant rise of the surface resistance of the studied crystals to the laser radiation damage. However, at a most fine polishing the value of the surface laser damage resistance was not higher than 40% with respect to the corresponding value of the bulk material. Considered were typical patterns of the damage center on the surface of crystals exposed to the laser radiation in connection with the structure and depth of the damaged layer. It was found that the degradation of a strongly damaged surface under the effect of laser radiation is accompanied by the emergence of the burned or melted material areas with no crystallographically oriented cracks formed. The typical pattern the surface of the laser damage center with a clearly pronounced crystallographic orientation of cracks approaches in its view the bulk damage as the degree of faultness of the subsurface layer decreases.!0