Development of a Power-Modulated Laser System with Long Pulse Duration and Its Application to Plasma Diagnostics

本研究的目的是证明驱动散射法的原理，该方法已被提出作为高温等离子体诊断的新方案。在驱动散射中，将功率调制激光束注入等离子体激发静电波。从激发波的色散特性可以估计等离子体的某些参数。1990年，研制了功率调制TEA CO_2激光系统。采用双模脉冲注入锁定方案，高概率获得功率调制（调制频率为30MHz）的10j级长脉冲持续时间为1mus数量级的输出。1991年，利用1990年研制的功率调制激光系统，在实验室等离子体中激发静电离子回旋波。Langmuie探针被用来探测等离子体波。采用一种新型的窄带宽数值滤波器从噪声背景中提取波信号。激发波的色散特性与静电离子回旋波的色散关系一致。1992年，将实验得到的波幅与理论分析和计算机模拟预测的波幅进行了比较。实验得到的波幅值与理论值在一个数量级内基本吻合，仿真结果与理论值吻合较好。

The objective of the present study is to prove the principles of the driven scattering method which has been proposed as a novel scheme for high temperature plasma diagnostics. In the driven scattering, a power-modulated laser beam is injected into the plasma to excite electrostatic waves. Certain plasma parameters can be evaluated from the dispersion character of the excited waves.In 1990, a power-modulated TEA CO_2 laser system was developed. Two-mode pulse injection locking scheme was adopted and a power-modulated (the modulation frequency of 30MHz, 10J-class outputs with long pulse durations of the order of 1mus were obtained with high probability.In 1991, electrostatic ion cyclotron waves were excited in a laboratory plasma by making use of the power-modulated laser system developed in 1990. Langmuie probes were used to detect the plasma waves. A newly developed numerical filter having a narrow bandwidth was used to extract the wave signal from noisy background. The dispersion character of the excited waves was consistent with the dispersion relation of the electrostatic ion cyclotron wave.In 1992, the wave amplitude obtained in the experiment was compared with those predicted by a theoretical analysis and computer simulation. The wave amplitude obtained experimentally roughly agreed with the theoretical value within an order of magnitude, while the simulation result agreed well with the theoretical value.