Characteristics of Pulsated Oscillation of Supersonic-flow Chemical Oxygen-Iodine Laser

超音速流动化学氧碘激光器(S线圈)有望成为高功率激光光源。利用调Q操作从S线圈中提取出极强的脉冲。为了开发和优化这种脉冲激光系统，需要对激光的光束质量、功率、时间依赖性等特性进行准确的评估。因此，本研究开发了激光光学数值模拟方法，计算程序由两部分组成，一部分是气体流动和化学反应的计算程序，另一部分是光学程序。由于这两部分现象的特征时间不同，后者的每300个时间步长与前者的1个时间步长相耦合。在前一部分中，用全隐式有限元…方法求解了三维可压缩的N-S方程和一个包含21个化学反应和12个化学组分的化学动力学模型更多的是差分法。空腔内的流动假定为喉道混合系统的下游，如前文[1]所示。在后半部分，引入了一个近轴波动方程来描述光束的衍射和干涉。从麦克斯韦方程出发，简化了两个假设，即激光束是单频的，且光束的传播方向几乎是轴的，从而得到了近轴波动方程。此外，为了考察衍射和干涉的影响，采用几何光学代替波动光学进行了另一次计算，结果表明，波动光学和几何光学的光束功率随时间的变化规律是相似的。峰值功率在振荡开始后90 ns处达到最大值。波动光学的峰值比几何光学的峰值小9%。计算得到的光束扩展角有所减小：25000 ns时的值比90 ns时的值小20%。这意味着，与连续提取相比，最大功率下的激光质量略差。较少

A supersonic-flow chemical oxygen-iodine laser (S-COIL) is expected to have outstanding potential as a high-power laser source. Extremely strong pulse would be extracted from the S-COIL by utilizing Q-switch operation. In order to develop and optimize this pulse laser system, characteristics of the laser such as beam quality, power, time-dependence, so on, should be accurately evaluated. Thus, in this study, numerical method is developed for simulating the laser optics.The calculation code consists of two parts one is a code for the gas flow and chemical reactions, and the other is that for the optics. Because of the difference of characteristic times between the phenomena in these two parts, every 300-time-steps of the latter calculation is coupled with one-time-step of the former. In the former part, three-dimensional, compressible Navier-Stokes equations and a chemical kinetic model encompassing 21 chemical reactions and 12 chemical species are solved by means of full-implicit finit … More e difference method. The flow in the cavity is assumed to be of the downstream of the throat mixing system, which is shown in the previous paper [1]. In the latter part, a paraxial wave equation is introduced so as to describe the diffraction and interference of the beam. The paraxial wave equation is derived from the Maxwell equation by simplifying with two assumptions that the laser beam is of single frequency, and that the propagating direction of it is almost axial. Additionally, another calculation adopting geometric optics instead of wave optics is conducted in order to examine the effects of diffraction and interference.The results indicate that the time dependence of the beam power is qualitatively similar between the wave and geometric optics. The peak power reaches to the maximum value at 90 ns after the initiation of oscillation. The peak value for the wave optics is 9 % less than that for the geometric optics. The calculated spreading angle of the beam is shown to decrease: its value at 25,000 ns is 20 % less than that at 90 ns. This means the laser quality at the maximum power is slightly worse compared to that of continuous extraction. Less