MODEL OF EXPLOSION-LIKE ACCUMULATION OF DEFECTS UNDER LASER DAMAGE OF BORATE SINGLE CRYSTALS

Abstract

The gradual accumulation of small structural changes induced by irradiation with many short-term relatively weak laser pulses leads to catastrophic destruction of materials, which is perhaps the main problem of resistance of materials to laser radiation. A typical phenomenon in multi-pulse laser destruction (BLR) of materials is a decrease in the number of laser pulses that lead to destruction, while increasing their power. At present, models that would satisfactorily explain the macroscopic destruction of materials of different nature due to the accumulation of microscopic structural changes are underdeveloped. Considerable attention in the study of BLR has been devoted to such a common semiconductor as silicon. In particular, it was found that there is a minimum level of radiation intensity , below which the destruction does not occur at any number of pulses. BLR has also been studied in transparent dielectrics, and the dependence of the critical number of pulses in the series on the intensity of laser radiation for transparent materials has the same form as in the case of media with absorption.

The model of the destruction of the semiconductor materials under the action of multi-pulse laser irradiation is extended to the transparent borate crystals belonging to the main materials of nonlinear optics. In that case, the point defects generation mechanism can be considered as thermal fluctuating one causing explosion-like accumulation of the defects. The mathematical description of the defect generation mechanism is presented. The point defect interaction with deformation field arising under multi-pulse laser irradiation was found. The defects themselves enhance such the interaction. Therefore, the energy of the defect’s formation is increasing due to the positive feedback in the process of the laser-induced defects generation.