重复频率激光放大器是实现重复频率激光器的关键器件,其重复频率取决于对抽运及放大过程中产生热量的有效控制。针对千焦耳量级输出重复频率激光器的需求,通过合理的结构设计、冷却液选型及测试等,研制出一台基于氙灯抽运、钕玻璃增益介质、液体冷却、通光直径为Φ130 mm的激光放大器样机。测试结果表明,该放大器样机可实现每分钟一次的重复频率运行,同时具备双程1.3189倍净增益,双程动态波前PV(peak to valley)平均值为0.2718波长(λ)(20 ℃,λ=1053 nm,10发次计)和0.3223λ(30 ℃,λ=1053 nm,10发次计)。

A model which can simulate the pump dynamics process of the main amplifiers in million joules laser facility is built based on Monte Carlo algorithm and a ASAP software. The model contains 3D airspace and 1D time domain, and the evolution of the distribution of the energy in light pass surface in different pumping time with complete absorption on cladding is calculated, which is the same with the results mentioned in previous articles proving the accuracy of the model. The comparisons of average small signal gain coefficient are made between the cases when the residual reflection in cladding is taken into consideration or not. The results show that there is no significant difference when residual reflectivity is below 0.05%. The value of calculated average small signal gain coefficient with residual reflection is 6 percentage smaller than the measured value(4.42/m), which results from the use of part approximation during the simulation, the unconsidered spectrum of spontaneous radiation,the subsurface damage in the actual Nd:phosphate glass and so on.

基于蒙特卡罗算法及ASAP 光学软件构建了完整分析万焦耳级激光主放大器抽运动力学过程的模型。该模型包含三维空域和一维时域，分析计算了包层完全吸收时不同抽运时刻通光面上的储能分布，其变化趋势与文献报道结果相同，验证了建模的正确性。通过对比包层完全吸收和部分剩余反射时的平均小信号增益系数，发现当剩余反射率低于0.05%时，两者区别并不明显。考虑包层部分反射后平均小信号增益系数的计算值比测量值4.42/m 偏小6%，分析其原因主要在于模型计算过程中的采用部分近似、未考虑自发辐射的光谱宽度以及钕玻璃中存在的亚表面缺陷等。

采用二维时域有限差分(FDTD)法，分析并对比了弯曲分叉部分的形状分别为正弦形和圆弧形的基于金属绝缘体金属（MIM）型表面等离子体光波导的Y形分束器的反射率、传输率以及能量分束比随几何结构参数的变化关系。数值计算表明，波导宽度对这两种Y形分束器传输特性的影响较为明显，两个输出分支的偏移量和弯曲分叉部分的长度对这两种Y形分束器传输特性的影响比较微弱。在600~1500 nm波长范围内，弯曲分叉部分为圆弧形的Y形分束器的传输特性比弯曲分叉部分为正弦形的好。对于非对称型Y形分束器，当弯曲分叉部分为正弦形时，偏移量对反射率、传输率和能量分束比的调节作用较为明显，能量分束比最大可达到2∶1。当弯曲分叉部分为圆弧形时，偏移量对反射率、传输率和能量分束比的调节作用较为微弱。