Theoretical Analysis and Control of Harmonic Generation Aimed at Applying to Electronics Implementation

非线性光学晶体波长转换技术是激光精密微加工的重要技术之一。关于重复辐照下谐波产生的传统研究进展大多是通过实验或经验进行的。关于它们的理论研究主要涉及单脉冲辐照或连续辐照下的稳态。波长转换必不可少的相位匹配对晶体温度敏感，晶体温度变化时转换效率下降。由于激光的吸收，晶体的温度发生变化。因此，用传统的理论分析方法无法分析晶体温度变化对波长转换的影响。在本研究中，考虑了重复照射下激光吸收的影响，进行了非稳态理论分析。首先，针对二次谐波的产生，在考虑激光吸收的情况下，推导了二次谐波产生的控制方程，并建立了与热传导方程的耦合分析模型。KDP和KTP被认为是非线性光学晶体。分析了聚焦效应引起的高入射脉冲强度对效率的促进作用。在此基础上，研究了最佳相匹配温度。结果表明，通过将相匹配温度调整到晶体内达到的最高温度，可以获得较高的转换效率。分析了波束发散角和重复频率对转换效率的影响。然而，通过仿真验证了该方法在不受它们影响的情况下获得了较高的转换效率。对硅吸收系数的温度依赖性测量、硅单晶的激光内部加工以及考虑多次反射和蒸发的激光打孔热流体力学分析等电子学应用方面的基础研究也进行了深入的研究。少

The wavelength conversion technology with nonlinear optical crystals is important for laser precision microfabrication. The conventional researches / developments about harmonic generation under repetitive irradiation have been conducted experimentally or empirically. Theoretical studies about them have dealt with single pulse irradiation or steady state under continuous irradiation. Phase matching that is indispensable for wavelength conversion is sensitive to the temperature of crystal, and conversion efficiency falls when its temperature is changed. The temperature of crystal is changed due to laser absorption. Therefore, it is impossible to analyze influence of the temperature change in the crystal on wavelength conversion by the conventional theoretical analysis.In this research, the non-steady state theoretical analysis considering the influence of laser absorption under repetitive irradiation was performed. First, about second harmonic generation, the governing equations of the … More harmonics generation were derived by considering laser absorption, and a coupling analysis model with the heat conduction equation was constructed. KDP and KTP were supposed as nonlinear optical crystals. Promotion of high efficiency by the high intensity of incident pulse caused by the focusing effect was also analyzed. Based on the constructed model, optimum phase matching temperature was investigated. As a result, it was found that the high conversion efficiency is achieved by tuning phase matching temperature to the maximum temperature reached in the crystal. It was clarified also that the conversion efficiency is affected by the beam divergence angle and the repetition frequency. However, according to the proposed method, it was confirmed by simulations that high conversion efficiency is obtained without receiving influence of them.Fundamental studies in electronics application, such as measurement of the temperature dependence of the absorption coefficient of silicon, the laser internal processing of silicon single crystal and thermohydrodynamics analysis of laser drilling by considering multiple reflection and evaporation were also performed. Less