碟片激光器泵浦均匀性的研究

发布时间：2018-11-23 20:21

【摘要】：碟片激光器泵浦光斑的均匀性是减小激光晶体热畸变、实现高光束质量、高平均功率、高光光转换效率激光输出的核心单元技术之一,也是碟片激光器优化设计难点所在。本文针对基于共轭双抛物面镜的多次泵浦结构,通过对泵浦源均匀性、抛物面镜单次聚焦光斑均匀性、多次泵浦空间重叠均匀性的深入分析,在综合考虑系统失调对泵浦均匀性影响的同时,开展碟片激光器多次泵浦系统的综合优化设计,并给出最佳设计方案,开展相应的实验研究。具体研究内容如下：第一,针对泵浦源的均匀性,通过对比分析微透镜阵列、柱面镜组、多边形匀化棒和方光纤四种匀化方案,结合多次泵浦系统光路结构特点,选择方光纤作为最佳方案。第二,针对单次聚焦光斑的均匀性,通过分析抛物面镜成像特性,指出聚焦光斑边沿像点弥散斑几何半径应小于150μm。第三,针对多次聚焦光斑的中心重合特性,通过分析抛物面镜自身光学特性、双抛物面镜失配以及碟片晶体离焦对各次聚焦光斑相对位置关系的影响,证明共轭双抛物面镜多次泵浦结构具有极好的多次泵浦稳定性,保证多个聚焦光斑几何中心的重合。第四,针对多次聚焦光斑的边沿重合特性,通过分析碟片晶体倾角和抛物面镜成像特性对聚焦光斑畸变的影响,指出畸变的本质原因是准直光束离轴入射抛物面镜导致离轴方向及其正交方向的成像垂轴放大率不相等,提出基于共焦点分段抛物面镜和一维扩束系统的两种光斑畸变校正方法,达到较好的校正效果。第五,提出一种加入直角棱镜的共轭双抛物面镜多次泵浦方案,通过合理设计实现系统中各项关键指标全局最优,设计出两套泵浦均匀性分别达到93.8%和96.31%、泵浦功率密度为4.3kW/cm2和5.48 kW/cm2.泵浦次数达20次和48次的多次泵浦系统。第六,对泵浦均匀性的各研究环节进行实验验证,最终在碟片晶体上获得了非常均匀的叠加泵浦光斑,基于两套多次泵浦系统进行CW碟片激光器运行实验,一套系统实现了M2≈1.3的高光束质量激光输出,输出功率125W,光光转换效率34.2%,另一套系统实现了654W的高平均功率激光输出和47.2%的高光光转换效率,光束质量M2≈7.2。
[Abstract]:The uniformity of laser spot pumped by disc laser is one of the core unit techniques to reduce the thermal distortion of laser crystal, achieve high beam quality, high average power and high optical conversion efficiency. It is also a difficult point in the optimization design of disc laser. In this paper, based on the conjugate double parabolic mirror, the uniformity of pump source, the uniformity of single focus spot of parabolic mirror and the overlap uniformity of multiple pumping space are analyzed. While considering the effect of system misalignment on pumping uniformity, the optimal design of disc laser multiple pumping system is carried out, and the optimal design scheme is given, and the corresponding experimental research is carried out. The main contents are as follows: first, aiming at the uniformity of pump source, four homogenization schemes, such as microlens array, cylindrical mirror group, polygonal homogenized rod and square fiber, are compared and analyzed. Choose square fiber as the best scheme. Secondly, in view of the uniformity of single focus spot, by analyzing the imaging characteristics of parabolic mirror, it is pointed out that the geometric radius of the focal spot edge diffusing spot should be less than 150 渭 m. Thirdly, according to the central coincidence characteristics of multi-focus spot, the effects of parabolic mirror's own optical properties, double parabolic mirror mismatch and disk crystal defocus on the relative position of each focusing spot are analyzed. It is proved that the multi-pump structure of conjugate double-parabolic mirror has excellent stability of multiple pumping, which ensures the coincidence of the geometric centers of the focusing spot. Fourthly, in view of the edge coincidence characteristics of multi-focus spot, the effects of crystal inclination and parabolic mirror imaging characteristics on focusing spot distortion are analyzed. It is pointed out that the essential reason of distortion is that the axial magnification of the imaging vertical axis in the off-axis direction and its orthogonal direction is not equal due to the off-axis incidence of the collimated beam and the parabolic mirror. Two correction methods of spot distortion based on common focus segmented parabolic mirror and one-dimensional beam expander system are proposed to achieve better correction effect. Fifthly, a multi-pump scheme of conjugate double-parabolic mirror with right-angle prism is proposed. The global optimum of the key indexes in the system is realized by reasonable design, and the pump uniformity of two sets is up to 93.8% and 96.31% respectively. Pump power density of 4.3kW/cm2 and 5.48 kW/cm2. Multiple pumping system with 20 and 48 pumping times. Sixth, the experimental verification of the pump uniformity is carried out. Finally, a very uniform superposition pump spot is obtained on the disk crystal. Based on two sets of multiple pumping systems, the CW disc laser operation experiment is carried out. One system achieves a high beam quality laser output of M2 鈮，

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