ガウシアンビーム照射による第二高調波発生効率の理論的解析

概要

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In recent years, the frequency conversion technique using nonlinear optical crystals are becoming more and more important for the applications of solid-state lasers to precision microfabricarion. For the first step of the study, we have analyzed the temperature dependence of SHG conversion efficiency theoretically, supposing uniform beam. The complex wave amplitude equations were derived, considering the absorption of laser in the crystal. The results were presented in the previous paper. In this paper, the analysis was carried out two-dimensionally with an axisymmetrical model based on the previous one-dimensional model, applying the paraxial approximation. Two-dimensional temperature distribution induced by laser absorption and variation of the conversion efficiency of KDP crystal were analyzed quantitatively during repetition irradiation of pulse laser. The influences of pulse width and beam intensity distribution were also investigated Main results are summarized as follows : (1) Depending on SHG and its inverse conversion, temperature of the crystal with Gaussian beam irradiation fluctuates remarkably in the axial direction. (2) During Gaussian beam irradiation, heat conduction in the radial direction prevents temperature from rising in the central part of crystal. (3) The conversion efficiency for a Gaussian beam stays relatively high for a long period, compared with that of uniform beam.
公益社団法人精密工学会の論文
2003-03-05