Development of an Infrared Thomson Scattering System for Diagnostics of Processing Plasmas

点击翻译按钮获取中文摘要

When laser Thomson scattering is applied to discharges using reactive gases, there is a strong possibility that the laser pulse may perturb the discharges. Most of the reactions that a laser might induce, such as photo-detachment of electrons from negative ions and photo-dissociation of molecules, have a photon energy threshold. This project aimed to develop a new Thomson scattering system based on an infrared (low photon energy) laser for diagnostics of reactive plasmas and to examine conditions that the laser pulse disturbs the discharges. Also, the improvement of the lower detection limit for electron density was performed. Following results were obtained.(1) A Thomson scattering measurement system based on a 1.064 μm wavelength YAG laser was constructed. Scattering measurements showed that the results were comparable with those obtained using previous Thomson scattering systems that used visible lasers.(2) No evidence of laser perturbation was observed of ICP discharges using CFィイD24ィエD2 gas. However, the laser perturbation was observed at a wavelength 532 nm for a microwave discharge plasma produced in CHィイD24ィエD2 gas at a pressure of 20 Torr. These phenomena should be investigated in detail hereafter.(3) The lower detection limit of electron density was improved down to 5x10ィイD115 ィエD1 mィイD1-3ィエD1. This was achieved mainly by maximizing the detection solid angle, increasing shot numbers for data accumulation, and using a monochromator which has a specific characteristic of high stray light rejection.