大能量空间全固态板条激光器的技术研究
文献类型：学位论文
| 作者 | 杨海龙 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 陈卫标 |
| 关键词 | 空间全固态激光器 Zig-zag板条 Porro棱镜谐振腔 腔内光束整形 可靠性 |
| 其他题名 | Study of high energy all-solid-state slab lasers for space applications |
| 中文摘要 | 近年来，随着星载激光雷达和空间激光通信的快速发展，对于空间激光器输出指标的需求也在进一步增长，高效率、高可靠性和大能量输出的空间激光器是一种发展趋势。 本论文重点开展了基于传导冷却的Zig-zag板条振荡器和放大器，以及激光器的效率提升技术、稳定性和可靠性方面的研究。首先介绍了空间激光器的应用背景，对国内外比较成功的空间全固态激光器进行了调研，罗列了激光器的主要技术参数。并分析了当前空间激光器的三个主要设计要点：晶体及热控、效率和可靠性。 介绍了Zig-zag板条晶体的特点以及两种不同的泵浦方式，选取了大能量输出、结构简单可靠的侧面方式泵浦Zig-zag板条。通过琼斯矩阵理论分析了高稳定性Porro棱镜的退偏特性，以及正交双Porro棱镜腔腔内激光的偏振态，并利用低电压驱动的电光调Q晶体实现谐振腔的偏振耦合输出。实验通过Zig-zag板条Porro棱镜谐振腔实现了73.8mJ的激光输出，光光转换效率为12.6%，，脉冲宽度为14ns，重复率为20Hz，光束质量水平方向M2为2.2，竖直方向为2.5。设计了Zig-zag板条晶体的单程放大器，模拟了板条截面对泵浦光的吸收分布，同时分析了LD不同巴条间距时板条的寄生振荡。通过放大器获得了341mJ的能量输出，脉宽为13ns，放大器的光光转换效率达到17%，光束质量水平方向M2为3.1，竖直方向为3.5。输出激光能量的不稳定度小于2%。设计了通过两级级联放大的实验来研究Zig-zag板条放大器对输出激光光束指向稳定性的影响。 为了提高空间激光器的倍频效率，选取了整形效率较高的径向双折射元件（RBE）腔内整形技术来输出平顶光束。理论计算推导出RBE整形系统中偏振片反射率的表达式和偏振片反射激光的光强分布。设计了基于正交双Porro棱镜谐振腔的腔内光束整形激光器，并理论模拟了谐振腔的自再现模。通过实验获得72.5mJ的平顶光束输出，脉宽为11ns，光光转换效率为17.3%，其光强分布与理论计算吻合。输出平顶光束的调制度为1.56:1，平顶光束的阶数为N=6。介绍了平顶光束的数学模型和倍频理论，设计了基于直通板条晶体的整形谐振腔进行倍频实验，通过谐振腔输出了62.9mJ的平顶光束。同时设计了传统输出高斯光束的激光谐振腔来对比KTP和LBO两种不同晶体的倍频效率。相同峰值功率密度下平顶光束的倍频效率更高，且对于有效非线性系数大的倍频晶体，平顶光束的效率提升效果更好。 针对空间激光器的可靠性，分析了光路失调对激光器输出性能的影响，设计了三种不同的谐振腔来对比输出激光能量的稳定性和光束指向的稳定性。理论分析了不同线偏振光在Zig-zag板条晶体的全内反射点的光场叠加效应，结果显示p偏振光的光场叠加效应最弱，而且增大Zig-zag板条晶体的传输反射角度也可以有效的降低光场叠加效应。理论计算了纵模间的增益比、频率差和相位差对纵模拍频的影响，其中增益比对激光输出脉冲波形的调制影响最大。设计了单Porro短腔被动调Q谐振腔，实现了1.55mJ、4.5ns、3Hz的单纵模脉冲激光输出，光束质量M2值为1.49。 面向未来空间的应用，提出了基于MOPA技术的20Hz、150mJ的绿光空间激光器的总体方案，设计了双Porro棱镜、单纵模平顶光束输出的谐振腔，以及两级Zig-zag板条放大器，并模拟计算了各级的输出能量 |
| 英文摘要 | In recent years, due to the rapid development of spaceborne lidar and space laser communication, the specification of spaceborne laser is needed to upgrade strongly. Spaceborne laser with high efficiency, high reliability and high output energy is a trend. In this dissertation, conductively cooling Zig-zag slab oscillators and amplifiers was focused on, and the efficiency, stability and reliability of the laser system was studied. First of all, the application background of spaceborne lasers was reviewed and some successful spaceborne solid-state lasers in the world were introduced. Three main design features of spaceborne lasers was analyzed, such as thermal controlling of the crystal, efficiency and reliability. Then the characteristics of the Zig-zag slab and two different ways of pumping were introduced. The way of side pumping with high output energy and high reliability was selected to do experiments. Jones matrix was used to analyze the phase shift of Porro prism and the polarization in the high stability crossed Porro prism resonator. A Q-swiched crystal with a low driving voltage was used to output with polarization coupling. The oscillator with Zig-zag slab and crossed Porro prisms provided output energy of 73.8mJ with 20Hz, the pulse width was 14ns, the beam quality was M_x^2=2.2 and M_y^2=2.5, and the optical-to-optical conversion efficiency is 12.6%. A single-pass Zig-zag slab amplifier was designed and the absorption distribution of the pump light in the slab was simulated. The parasitic oscillation of the slab with different distances of LDA’s bars was analyzed. The output energy of 341 mJ was obtained from the amplifier and the pulse width was 13 ns. The optical-to-optical conversion efficiency is 17% and the beam quality was M_x^2=3.1 and M_y^2=3.5. The output energy instability was less than 2%. In addition, two Zig-zag slab amplifiers were designed to study the beam pointing stability of the whole system. In order to improve the doubling frequency efficiency of spaceborne lasers, the intra-cavity beam shaping system with RBE was selected to output flat-top beam. The reflectivity and the reflected light intensity distribution of the polarizer in the shaping system were derived. The intra-cavity beam shaping resonator with Porro prism was designed and the self-reproduction mode in the cavity was calculated. A flat-top beam with 72.5mJ was obtained in the experiment. The pulse width was 11ns and the optical-to-optical conversion efficiency was 17.3%. The measured profile of the output beam was consistent with the result of theoretical calculations. The modulation of the output flat-top beam was 1.56:1 and the flat-top order was N=6. Mathematical model and double-frequency theory of flat-top beams was introduced. A straight slab beam shaping laser with 62.9mJ was designed to frequency doubling comparing with the traditional Gaussian beam. The double frequency efficiency of flat-top beam was higher than that of Gaussian beam with the same peak power density. The effect of improving double frequency efficiency with flat-top beam was better than that of Gaussian beam when the effective nonlinear coefficient of the crystal was larger. The impact of a laser output performance from optical path imbalance was discussed and three different resonator were designed to compare the stability of the output laser energy and beam pointing. The optical superposition effect of the total internal reflection point in the Zig-zag slab was discussed with different polarized lasers. The results showed that the superposition effect of p-polarization was the weakest. It also showed that increasing the reflection angle of the slab could effectively reduce the superposition effect. The frequency beating between the longitudinal modes from gain ratio, frequency and phase difference was analyzed and gain ratio was the most important. A single Porro prism passively Q-switched resonator with short cavity length was designed to output single longitudinal mode. The output energy was 1.55mJ with 3Hz. The pulse width was 4.5ns and the beam quality was M^2=1.49. For future space applications, a program of a 20Hz and 150mJ green space laser with MOPA technique was proposed. A Porro prism resonator with single longitudinal mode and flat-top beam was designed. Two Zig-zag slabs were used as amplifiers and the output energy with each level was simulated. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15987]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 杨海龙. 大能量空间全固态板条激光器的技术研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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