LD侧面泵浦多晶Nd：YAG陶瓷BBO电光调Q窄脉宽绿光、紫外光激光器研究

【作者】 白杨；

【导师】 白晋涛；

【作者基本信息】 西北大学 ， 光学， 2010， 博士

【摘要】 将半导体激光阵列侧面泵浦增益介质技术、非线性频率转换技术、调Q技术结合起来的新型全固态激光器可以实现高功率、高重复率、窄脉冲宽度、波长范围从中远红外—可见光—深紫外的高质量脉冲激光输出,并且与气体、液体、化学、自由电子等传统激光器相比,具有结构紧凑、能量转换效率高、可靠性高、重量轻、光束质量好等优点,因此一直处于激光科学技术研究的前沿,并已广泛应用于工业精密加工、医疗卫生、激光通信、激光雷达、激光测距、热核反应等诸多领域。为获得高重复频率、高峰值功率、窄脉冲宽度的532nm绿激光和高单脉冲能量、高峰值功率、窄脉冲宽度的355nm和频紫外激光及266nm四倍频紫外激光,本论文进行如下相关理论和实验研究：1.对LD多向侧面泵浦多晶Nd：YAG陶瓷棒中的泵浦光强度分布情况进行模拟。以LD五向泵浦为例,数值模拟了不同激光陶瓷棒半径、不同吸收系数及不同泵浦光会聚光斑半径条件下LD泵浦光在陶瓷棒内分布均匀性的变化规律和激光陶瓷棒内部的温度分布情况；利用矩阵对连续LD侧面泵浦的Nd：YAG陶瓷的热透镜焦距进行了推导,计算出了不同泵浦功率下多晶Nd：YAG陶瓷棒的热透镜焦距；设计了一种测量LD侧面泵浦的激光陶瓷棒的热透镜焦距的简单方法。2.从电光调Q速率方程出发,建立了电光调Q激光输出特性变量模型；针对电光晶体的温度场分布和热应力分布建立了热传导理论模型和热弹性力学模型；采用有限元分析法,通过对KD*P、LiNbO3、BBO和RTP四种常用的的温度分布和热应力分布进行模拟和分析,选择BBO电光晶体用于本论文实验研究。3.基于折射率方程,对KTP和LBO两种晶体倍频1064nm基频光产生532nm绿光的相位匹配曲线、有效非线性倍频系数、走离角的空间分布特性进行了数值模拟和理论分析,获得了Ⅰ类、Ⅱ类角度相位匹配的KTP晶体和LBO晶体的最佳相位匹配方向(最佳相位匹配角)、有效非线性倍频光学系数和沿最佳相位匹配方向上的走离角,并通过对比分析,选择LBO晶体用于本论文倍频实验研究。4.完成了连续LD侧面泵浦Nd:YAG陶瓷／BBO电光调Q／LBO腔内倍频的高重复率、高功率、窄脉宽绿光激光器实验研究。从V型折叠谐振腔的像散问题的理论分析入手,利用谐振腔结构设计软件对V型谐振腔进行了像散补偿、稳定性的结构优化设计；其次采用模拟设计出的谐振腔结构参数,在电光调Q最佳重复率为10.2kHz时,获得了最大平均功率为32.6W、最窄脉冲宽度为58.5ns的s线偏振的准连续绿激光输出。5.完成了脉冲LD侧面泵浦Nd:YAG陶瓷／BBO电光调Q／LBO腔外倍频高能量、高峰值功率、窄脉宽紫外激光器实验研究。①当LD泵浦电流为120A、重复率为1Hz时,获得了最大单脉冲能量为23.4mJ,最短脉冲宽度为5.25ns、最高峰值功率为4.46MW的355nm窄脉宽紫外激光输出；在重复率为20Hz时,355nm紫外脉冲激光的最高平均功率达到245.6mW、脉冲宽度11.2ns、最高峰值功率达到1.1MW,并利用分光镜,同时获得了663.6mW的1064nm脉冲红外光和335.5mW的532nm脉冲绿激光输出。②在此基础上,将和频晶体更换为Ⅰ类BBO四倍频晶体,当LD泵浦电流为120A、重复率为1Hz时,获得了最大单脉冲能量为18.4mJ,最短脉冲宽度为4.66ns、最高峰值功率为3.95MW的266nm窄脉宽紫外激光输出；在重复率为20Hz时,266nm紫外脉冲激光的最高平均功率达到185.5mW、脉冲宽度10.1ns、最高峰值功率达到0.92MW,同样利用分光镜,获得了820.2mW 1064nm脉冲红外光和384.5mW的532nm脉冲绿激光输出。更多还原

【Abstract】 The combining of semiconductor laser array with technology of side-pumping laser gain medium, nonlinear frequency conversion and Q-switching make the novel all-solid-state laser can achieve high power, high repetition rate arid narrow pulse width high qualified laser pulse with the wavelength range from far infrared-visible light to deep-UV. The novel all-solid-state laser has advantages of compact structure, high energy conversion efficiency, high reliability, light weight and good beam quality compared with other traditional lasers such as gas, chemical and free electric laser devices, so it is always used in the forefront of laser science and technology research and has been widely used in industrial precision machining, medical treatment, laser communication, laser radar, laser ranging, thermonuclear reaction and many other areas.In order to obtain the high peak power, high repetition rate, narrow pulse width green laser at 532nm and the UV laser at 355nm with high pulse energy, narrow pulse width, in addition the high quality stable output deep UV 266nm laser the theoretical and experimental researches in the article worked as follows:1. Simulated the light intensity distribution in the LD multi-side-pumped Nd:YAG ceramic rod. Take LD pumping in 5 directions as the example:the thermal scattering and the distribution variation law of LD pump light in ceramic rod was simulated in different conditions of rod radius, absorption and convergent pump light spot radius; the lengths of thermal lensing of the LD continuously pumped ceramic rod was derived through matrix, the lengths of the thermal lens were carried out under different pumping power; a simple method to measure the thermal length of laser ceramic rod lens was designed and it was used in polycrystalline Nd:YAG ceramic rod, which can be pumped by 808nm laser at the maximum power of 300 watts, thermal lens length measuring.2. A model for laser output character variation was established based on rate equation of electro-optical Q switching. Models of theoretical heat transport and thermo elasticity were established for demonstrating temperature distribution and thermal stress in the electro-optical crystal. After the simulating and analysis of temperature distribution and thermal stress in these four type normal crystal KD*P, LiNbO3, BBO and RTP by finite element analysis method, BBO electro-optical crystal was chosen for the experiment.3. Based on the refractive index equation, the phase-matching curve, effective nonlinear frequency-doubling coefficient and discrete angle spatial distribution characteristics of 532nm green laser, which come from 1064nm fundamental light frequency-doubled through KTP or LBO were simulated and analyzed in the experiment; then the best phase-matching orientation,which is also called the best phase-matching angle, in KTP and LBO crystal for typeⅠand typeⅡwere got, and so did the effective nonlinear frequency-doubling optical coefficient and the walk-off angle along the best phase matching direction. Finally LBO was chosen for the experimental research after comparison and analysis.4. Waged the experimental study on BBO electro-optical Q switched high-repetition-rate, high power and narrow pulse green laser that generated by LBO intracavity frequency doubling continuous LD side-pumped Nd:YAG ceramic. From the theoretical analysis of astigmatism problem in V-folded resonator, the resonant cavity structural design software was used for V-cavity astigmatism compensation, stability and structural optimization design; then by parameters of the resonant cavity structure simulating s polarized quasi-continuous green laser achieved the maximum average of 32.6 W and 58.5 ns pulse width during the best electro-optic Q-repetition rate of 10.2 KHz.5. Finished the experimental study on LD pulsing side-pumped Nd:YAG ceramic/BBO electro-optical switched/LBO outer extra-cavity frequency doubling UV laser with high energy and peak power with narrow pulse width.①By using linear resonant cavity, pulsed LD side-pumped polycrystalline Nd:YAG ceramic, BBO electro-optical BBO synchronous switching, LBO outer extra-cavity frequency doubling & summing technology 355 nm UV narrow pulse of 5.25ns with maximal single pulse energy at 23.4 mJ and highest peak power at 4.46MW was obtained during at the pump current at of 120 A and Q switch repetition rate at of 1 Hz; when at the repetition rate of 20 Hz, the maximal average and peak power of 355 nm pulse respectively achieved 245.6 mW and 1.1 MW and its pulse width is about 11.2 nm wide, the 1064 nm infrared laser pulse at of 663.6 mW and 532 nm green laser pulse at of 335.5 mW was gained obtained simultaneously by using a spectroscope.②Based on the mentioned above, when replacing frequency summing crystal with typeⅠBBO, which used as 4 times frequency doubling crystal, the 266 nm UV pulse width of 4.66 ns pulse laser was generated at the pump current of 120A and repetition rate at of 1 Hz, its maximal single pulse energy and peak power are respectively 18.4 mJ and 3.95 MW; during the repetition rate varying to 20 Hz the width of 266 nm UV pulse is 10.1ns and the maximal average power and peak power respectively achieved 185.5 mW and 0.92 MW, the 1064 nm infrared laser pulse at 820.2 mW and 532 nm green laser pulse at 384.5 mW was obtained by using a spectroscope.更多还原