【摘要】：光束質(zhì)量是激光在實際應(yīng)用中非常關(guān)鍵的因素。然而在激光放大器中由于熱致畸變效應(yīng)的存在,通常情況下在放大過程中激光光束質(zhì)量會持續(xù)惡化。本文通過研究端面泵浦Nd:YVO4固體激光器中的熱效應(yīng)以及腔內(nèi)波前球差自再現(xiàn)的過程,提出并驗證了一種使用激光放大器動態(tài)補(bǔ)償光束質(zhì)量的方法。本文研究內(nèi)容主要分為兩部分,第一部分中進(jìn)一步完善激光振蕩器中的光束傳輸理論,用數(shù)值模擬和實驗驗證計算和分析激光振蕩級中光場復(fù)振幅分布和光束質(zhì)量的演化過程；第二部分是根據(jù)腔內(nèi)波前自再現(xiàn)的理論提出腔外用放大級動態(tài)補(bǔ)償光束質(zhì)量,驗證這一方法的有效性,并提出激光放大器中實現(xiàn)光束質(zhì)量動態(tài)補(bǔ)償?shù)脑砗头椒ā５谝徊糠种?首先從熱傳導(dǎo)方程出發(fā)計算端面泵浦下Nd:YVO4晶體的熱分布情況,并以此計算得出由熱分布導(dǎo)致的折射率分布并引起的熱致球差效應(yīng)。并對晶體熱效應(yīng)對高斯光束的影響做了研究,發(fā)現(xiàn)在高功率激光下因為增益飽和效應(yīng)的存在,晶體熱球差成為影響光束質(zhì)量最關(guān)鍵的因素,通過波前的補(bǔ)償是實現(xiàn)光束質(zhì)量的提高的有效方法。同時研究發(fā)現(xiàn)帶有正球差的光束在通過束腰之后球差符號發(fā)生了變化,即正球差可以變?yōu)樨?fù)球差,據(jù)此提出了波前球差在諧振腔內(nèi)部的自再現(xiàn)演化過程的理論模型,并用Matlab的模擬仿真和測量裝置的搭建驗證了理論模型的正確性。第二部分中通過分析激光振蕩器中球差自再現(xiàn)的現(xiàn)象提出一種使用激光放大器中晶體的正球差來動態(tài)補(bǔ)償光束質(zhì)量的方法,即將激光振蕩級中球差系數(shù)為負(fù)且絕對值最大的地方成像出來通過激光放大級,通過調(diào)節(jié)激光放大級的泵浦電流來動態(tài)調(diào)節(jié)激光放大級中激光增益介質(zhì)的正球差系數(shù),實現(xiàn)光束質(zhì)量的動態(tài)補(bǔ)償。然后搭建了相應(yīng)實驗裝置并進(jìn)行了波前、強(qiáng)度以及光束質(zhì)量的測量。隨著激光放大級泵浦功率的增大,可以找到一個合適的功率,使得光束質(zhì)量補(bǔ)償?shù)帽容^好,同時也搭建了對比實驗對理論進(jìn)行了驗證。最后在放大級泵浦功率為63W時,將振蕩級輸出的M2為4.2的光束補(bǔ)償至1.6,在放大光束功率的同時實現(xiàn)了光束質(zhì)量的補(bǔ)償。
[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.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TN722

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相關(guān)期刊論文 前1條

1 董延濤;趙智剛;劉崇;陳軍;;熱效應(yīng)對固體激光器偏振特性和基模輸出特性的影響[J];中國激光;2009年07期

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本文編號：2270716