激光放大器对光束质量的动态补偿
发布时间：2018-10-14 14:14
【摘要】：光束质量是激光在实际应用中非常关键的因素。然而在激光放大器中由于热致畸变效应的存在,通常情况下在放大过程中激光光束质量会持续恶化。本文通过研究端面泵浦Nd:YVO4固体激光器中的热效应以及腔内波前球差自再现的过程,提出并验证了一种使用激光放大器动态补偿光束质量的方法。本文研究内容主要分为两部分,第一部分中进一步完善激光振荡器中的光束传输理论,用数值模拟和实验验证计算和分析激光振荡级中光场复振幅分布和光束质量的演化过程；第二部分是根据腔内波前自再现的理论提出腔外用放大级动态补偿光束质量,验证这一方法的有效性,并提出激光放大器中实现光束质量动态补偿的原理和方法。第一部分中,首先从热传导方程出发计算端面泵浦下Nd:YVO4晶体的热分布情况,并以此计算得出由热分布导致的折射率分布并引起的热致球差效应。并对晶体热效应对高斯光束的影响做了研究,发现在高功率激光下因为增益饱和效应的存在,晶体热球差成为影响光束质量最关键的因素,通过波前的补偿是实现光束质量的提高的有效方法。同时研究发现带有正球差的光束在通过束腰之后球差符号发生了变化,即正球差可以变为负球差,据此提出了波前球差在谐振腔内部的自再现演化过程的理论模型,并用Matlab的模拟仿真和测量装置的搭建验证了理论模型的正确性。第二部分中通过分析激光振荡器中球差自再现的现象提出一种使用激光放大器中晶体的正球差来动态补偿光束质量的方法,即将激光振荡级中球差系数为负且绝对值最大的地方成像出来通过激光放大级,通过调节激光放大级的泵浦电流来动态调节激光放大级中激光增益介质的正球差系数,实现光束质量的动态补偿。然后搭建了相应实验装置并进行了波前、强度以及光束质量的测量。随着激光放大级泵浦功率的增大,可以找到一个合适的功率,使得光束质量补偿得比较好,同时也搭建了对比实验对理论进行了验证。最后在放大级泵浦功率为63W时,将振荡级输出的M2为4.2的光束补偿至1.6,在放大光束功率的同时实现了光束质量的补偿。
[Abstract]:Beam quality is a key factor in the practical application of laser. However, due to the existence of thermal teratogenic effect in laser amplifiers, the quality of laser beams will continue to deteriorate in the process of amplification. In this paper, by studying the thermal effect in the end-pumped Nd:YVO4 solid-state laser and the self-reproducing process of the spherical aberration in the cavity wavefront, a method of dynamically compensating the beam quality with the laser amplifier is proposed and verified. This paper is divided into two parts. In the first part, the theory of beam propagation in laser oscillator is further improved, and the complex amplitude distribution and the evolution process of beam quality in laser oscillation stage are calculated and analyzed by numerical simulation and experiment. In the second part, according to the theory of intracavity wave front self-reproducing, the beam quality is compensated by the external amplifier stage, which verifies the effectiveness of this method, and proposes the principle and method of dynamic beam quality compensation in laser amplifier. In the first part, the heat distribution of Nd:YVO4 crystal under end-pumped is calculated from the heat conduction equation, and the refractive index distribution caused by the thermal distribution and the thermo-induced spherical aberration effect are calculated. The influence of crystal thermal effect on Gao Si beam is also studied. It is found that the thermal spherical aberration of crystal becomes the most important factor affecting the beam quality because of the gain saturation effect in high power laser. The compensation through the wavefront is an effective method to improve the beam quality. At the same time, it is found that the spherical aberration symbol of the beam with positive spherical aberration changes after passing through the beam waist, that is, the positive spherical aberration can be changed into negative spherical aberration. Based on this, a theoretical model of the self-reproducing evolution process of the wavefront spherical aberration in the resonator is proposed. The correctness of the theoretical model is verified by the simulation of Matlab and the construction of measuring device. In the second part, by analyzing the phenomenon of spherical aberration self-reproduction in the laser oscillator, a method of dynamically compensating the beam quality by using the positive spherical aberration of the crystal in the laser amplifier is proposed. That is, where the spherical aberration coefficient is negative and the absolute value is the largest in the laser oscillation stage, the positive spherical aberration coefficient of the laser gain medium in the laser amplifier stage is dynamically adjusted by adjusting the pump current of the laser amplification stage. The dynamic compensation of beam quality is realized. Then the corresponding experimental device is built and the wavefront, intensity and beam quality are measured. With the increase of laser amplifying stage pump power, a suitable power can be found, which makes the beam quality compensation better. At the same time, a comparative experiment is built to verify the theory. Finally, when the pump power is 63 W, the beam with M2 4.2 output from the oscillation stage is compensated to 1.6, and the beam quality compensation is realized while amplifying the beam power.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN722
本文编号：2270716
[Abstract]:Beam quality is a key factor in the practical application of laser. However, due to the existence of thermal teratogenic effect in laser amplifiers, the quality of laser beams will continue to deteriorate in the process of amplification. In this paper, by studying the thermal effect in the end-pumped Nd:YVO4 solid-state laser and the self-reproducing process of the spherical aberration in the cavity wavefront, a method of dynamically compensating the beam quality with the laser amplifier is proposed and verified. This paper is divided into two parts. In the first part, the theory of beam propagation in laser oscillator is further improved, and the complex amplitude distribution and the evolution process of beam quality in laser oscillation stage are calculated and analyzed by numerical simulation and experiment. In the second part, according to the theory of intracavity wave front self-reproducing, the beam quality is compensated by the external amplifier stage, which verifies the effectiveness of this method, and proposes the principle and method of dynamic beam quality compensation in laser amplifier. In the first part, the heat distribution of Nd:YVO4 crystal under end-pumped is calculated from the heat conduction equation, and the refractive index distribution caused by the thermal distribution and the thermo-induced spherical aberration effect are calculated. The influence of crystal thermal effect on Gao Si beam is also studied. It is found that the thermal spherical aberration of crystal becomes the most important factor affecting the beam quality because of the gain saturation effect in high power laser. The compensation through the wavefront is an effective method to improve the beam quality. At the same time, it is found that the spherical aberration symbol of the beam with positive spherical aberration changes after passing through the beam waist, that is, the positive spherical aberration can be changed into negative spherical aberration. Based on this, a theoretical model of the self-reproducing evolution process of the wavefront spherical aberration in the resonator is proposed. The correctness of the theoretical model is verified by the simulation of Matlab and the construction of measuring device. In the second part, by analyzing the phenomenon of spherical aberration self-reproduction in the laser oscillator, a method of dynamically compensating the beam quality by using the positive spherical aberration of the crystal in the laser amplifier is proposed. That is, where the spherical aberration coefficient is negative and the absolute value is the largest in the laser oscillation stage, the positive spherical aberration coefficient of the laser gain medium in the laser amplifier stage is dynamically adjusted by adjusting the pump current of the laser amplification stage. The dynamic compensation of beam quality is realized. Then the corresponding experimental device is built and the wavefront, intensity and beam quality are measured. With the increase of laser amplifying stage pump power, a suitable power can be found, which makes the beam quality compensation better. At the same time, a comparative experiment is built to verify the theory. Finally, when the pump power is 63 W, the beam with M2 4.2 output from the oscillation stage is compensated to 1.6, and the beam quality compensation is realized while amplifying the beam power.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN722
【参考文献】
相关期刊论文 前1条
1 董延涛;赵智刚;刘崇;陈军;;热效应对固体激光器偏振特性和基模输出特性的影响[J];中国激光;2009年07期
，本文编号：2270716
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