设计了一种测量电容耦合等离子体电子密度时间演化的YAG激光汤姆孙散射系统。电容耦合等离子体是在真空条件下由300 W射频电源供电的板极装置中产生的。采用最大转换增益5.0×10 5 V/W的硅雪崩光电二极管(APD)测量波长范围为200~1000 nm的Nd∶YAG激光汤姆孙散射信号。为了提高汤姆孙散射信号强度,在等离子体发生器两侧设置一个光学振荡腔,用于加长驱动激光与等离子体地接触长度和放大汤姆孙散射信号,提高信号光的总发射强度。此外,在APD前端还设置了信号采集系统和多级滤波系统,以提高信噪比。最后,依据汤姆孙散射原理设计计算等离子体电子密度的反演算法,并将计算结果与朗缪尔探针的测量结果进行了对比,验证了该算法的有效性。

The YAG laser Thomson scattering system is designed to measure the time evolution of electron density of capacitive-coupled plasma (CCP). CCP is generated in a plate electrode device under vacuum which is powered by 300 W radio-frequency power supply. A silicon avalanche photodiode (APD) with a max conversion gain of 5.0×10 ⁵ V/W is used to measure the Nd∶YAG laser Thomson scattered signal in the wavelength range of 200 nm to1000 nm. In order to increase the intensity of the Thomson scattering signal, an optical oscillating cavity is set on both sides of the plasma generator to extend the contact length between the driving laser and the plasma and to amplify the Thomson scattering signal to increase the total emission intensity of the signal light. In addition, a signal collection system and a multistage filter system are positioned at the front-end of APD to improve the signal-to-noise ratio. Finally, we develop an inverse algorithm to calculate electron density of CCP based on the Thomson scattering principle, and the calculation results are compared with the measurement results of the Langmuir probe, which verifies the effectiveness of the algorithm.