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

利用非线性光学晶体实现波长转换是激光精密微加工的重要技术。关于重复辐照下谐波产生的传统研究/发展已经进行了实验或经验。对它们的理论研究主要涉及单脉冲辐照或稳态连续辐照。相位匹配是波长转换中必不可少的环节，但相位匹配对晶体的温度敏感，温度变化会导致转换效率福尔斯下降。晶体对激光的吸收使晶体的温度发生变化。因此，无法通过传统的理论分析来分析晶体内的温度变化对波长转换的影响，本研究考虑了重复照射下的激光吸收的影响，进行了非稳态理论分析。首先，关于二次谐波产生， ...更多信息 在考虑激光吸收的情况下，推导了谐波的产生公式，并建立了与热传导方程耦合的分析模型。KDP和KTP被认为是非线性光学晶体。分析了聚焦效应产生的高强度入射脉冲对高效率的促进作用。在此基础上，研究了最佳相匹配温度。结果发现，通过将相位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。还阐明了转换效率受光束发散角和重复频率的影响。然而，根据该方法，通过模拟可以确认，在不受上述影响的情况下，可以获得高的转换效率。此外，还进行了硅的吸收系数的温度依赖性的测定、硅单晶的激光内部加工、考虑多次反射和蒸发的激光打孔的热流体力学分析等电子学应用的基础研究。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