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

超音速流化学氧碘激光器（S-COIL）作为一种高功率激光源具有很大的发展潜力。利用Q开关操作，从S-线圈中提取极强脉冲。为了开发和优化这种脉冲激光系统，激光器的特性，如光束质量，功率，时间依赖性等，应该准确地评估。因此，本研究发展了一套模拟激光光学的数值方法，其计算程序由两部分组成，一部分是气体流动和化学反应程序，另一部分是光学程序。由于这两部分现象的特征时间不同，后者的计算每300个时间步与前者的一个时间步耦合。第一部分采用全隐式有限差分法求解三维可压缩Navier-Stokes方程和包含21个化学反应和12种化学组分的化学动力学模型， 关于我们 e差分法。空腔内的流动被假定为喉部混合系统的下游，这在以前的文章[1]中已经显示。在后一部分中，我们引入了一个傍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，在激光束为单频光束和光束传播方向近似为轴向的两个假设下，进行简化，导出了近轴波动方程。另外，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计算，结果表明，在波动光学和几何光学中，光束功率的时间依赖性在性质上是相似的。在振荡开始后90 ns，峰值功率达到最大值。波动光学的峰值比几何光学的峰值小9%。计算的光束扩展角显示出减小：其值在25，000 ns处比在90 ns处小20%。这意味着与连续提取相比，最大功率下的激光质量略差。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