超短激光脉冲与CsLiB₆O₁₀晶体相互作用的光学性质研究

【作者】 韩秀友；

【导师】 王丽；

【作者基本信息】 河北师范大学 ， 凝聚态物理， 2003， 硕士

【摘要】 论文从理论上对超短激光脉冲与非线性CsLiB₆O₁₀（CLBO）晶体相互作用的光学性质进行了研究。在皮秒和飞秒时域，由于泵浦光与产生的信号光的持续时间特别短，故在讨论超短脉冲与物质相互作用时必须计及超短脉冲在介质中传输的特殊性质，尤其是群速失配与群速色散引起的脉冲展宽。紫外波段激光的输出主要采用频率变换技术来实现，因此一种好的非线性光学晶体对于产生新的波长是非常重要的。与常用的KH₂PO₄（KDP）、β-BaB₂O₅（BBO）、LiB₃O₅（LBO）比较，CLBO晶体具有有效非线性系数大、输出波长范围宽、走离角小、允许参量范围宽、易生成大体积单晶等突出优点。论文完成了超短脉冲激光在CLBO晶体中传播特性的分析，并对CLBO晶体的超短脉冲参量特性进行了理论分析和数值模拟。 第一章介绍了超短激光脉冲的产生及发展状况，综述了CLBO晶体的研制背景及光学性质的研究进展情况。第二章对超短脉冲在CLBO晶体中的传播特性进行了理论研究。给出了折射率、群速指数、低阶和二阶色散系数随波长变化的关系曲线，研究了高斯脉冲、超高斯脉冲和双曲正割脉冲等超短脉冲在CLBO晶体中传播时，由于低阶色散和高阶色散引起的脉冲展宽和形变。第三章对CLBO晶体超短脉冲的参量特性进行了理论计算和数值模拟。从动量守恒、能量守恒出发推导得出了超短脉冲倍频的Ⅰ类、Ⅱ类相位匹配和群速匹配条件，对CLBO晶体用于超短脉冲倍频时的群速延迟以及由群速延迟决定的晶体长度进行了分析和数值模拟，并与BBO晶体进行了比较。以波长为532nm基波为例，数值模拟了经过不同长度的CLBO晶体后谐波的脉冲波形，及脉冲宽度随晶体长度的变化。从三波耦合方程出发，对CLBO用于皮秒级光参量放大时，最佳晶体长度、转换效率和参量光的脉冲宽度进行了理论分析和数值模拟，结果表明CLBO晶体适合在短波范围作光参量放大，为达到高的转换效率和窄脉宽的信号光输出，泵浦光和初始入射信号光的强度应根据晶体长度取最优化值。更多还原

【Abstract】 We have studied theoretically the optical properties of the interaction between ultrashort pulses and the nonlinear optics crystal cesium lithium borate (CsLiB₆O₁₀). In the picosecond and femtosecond time field, the durations of the pump and signal pulses are so short that special propagating characteristics of ultrashort pulse laser should be taken into account, especially the pulse broadening induced by the group velocity mismatch and the group velocity dispersion. We all know that the output of ultraviolet （UV） laser mostly depends on the conversion of nonlinear frequency, thus a new kind of excellent nonlinear optics （NLO） crystal is very important for the output of new wavelength. Compared with the usual crystals, such as KH₂PO₄ （KDP） , β -BaB₂O₅ （BBO） and LiB₃O₅ （LBO） , the CLBO crystal provides larger effective nonlinear coefficient, wider output wavelength range, smaller walk-off angle, wider permitted parameters, larger bulk crystal and many other advantages, which make it become an attractive NLO crystal for generating UV radiation. We have studied the propagating properties of ultrashort pulses in the CLBO crystal, analyzed theoretically and simulated numerically the optical parametric properties of interaction between ultrashort pulses and the CLBO crystal.In the chapter 1, we have introduced the development of ultrashort pulse laser and summarized the background and resent research advance of CLBO. In the chapter 2, we have studied theoretically the propagating characteristics of ultrashort pulses in the CLBO crystal. We have calculated and plotted the curves of the refractive index, group velocity index, lowest-order and second-order dispersion indexes as a function of wavelength. Thelowest-order and higher-order dispersion-induced broadening and deforming of light pulses is analyzed for various pulse shapes, such as Gaussian, super-Gaussian and hyperbolic secant pulses. In the chapter 3, we have analyzed and simulated the optical parametric properties of ultrashort pulses in the CLBO crystal. The phase matching and group velocity matching conditions of type-I and type-II second harmonic generation （SHG） are obtained according to the momentum and energy conservation laws. The group velocity delay of ultrashort pulse SHG on CLBO and the crystal length decided by the group velocity delay are analyzed and compared with BBO’s. Second harmonic is generated by 532nm fundamental wave on CLBO, and the harmonic pulse is plotted along with the CLBO crystal length. From three-wave coupling equations, the optimal crystal length, conversion efficiency and parametric light pulse width are computed numerically when CLBO is used in picosecond optical parametric amplification. The results present that CLBO are suited for optical parametric amplification in short wave band. In order to get higher conversion efficiency, the crystal length should be optimized according to the intensities of pump and signal waves.更多还原