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细加工的重要技术。传统的关于重复辐射下的谐波产生的研究/发展都是通过实验或经验来进行的。有关它们的理论研究已经涉及到单脉冲辐照或连续辐照下的稳态辐照。对于波长转换来说，相位匹配是必不可少的，它对晶体的温度很敏感，当温度变化时，转换效率下降。晶体的温度由于激光的吸收而发生变化。因此，用常规的理论分析方法无法分析晶体中温度变化对波长转换的影响。首先，关于二次谐波产生，…的控制方程在考虑激光吸收的情况下，得到了更多的谐波产生，并与热传导方程建立了耦合分析模型。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强度入射脉冲对高效率的促进作用。基于所建立的模型，研究了最佳的位相匹配温度。结果发现，通过将位相匹配温度调节到晶体中达到的最高温度，可以实现高转换效率。讨论了光束发散角和重复频率对转换效率的影响。在此基础上，进行了硅单晶吸收系数随温度变化的测量、硅单晶激光内部加工以及考虑多次反射和蒸发的激光打孔热力学分析等电子应用基础研究。较少

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