Laser-Induced Flourescences due to the Stark-Forbidden and the Electric Quadrupole Transitions in a Discharge Plasma

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The purpose of this research is to observe in detail the laser-induced fluorescence associated with the Stark-forbidden and the electric quatrupole transitions in a hollow cathode discharge and to develop new diagnostics for electric field distribution in the sheath with applications of the laser-induced fluorescence observation. Our main results are as follows :1.Polarization of the fluorescences associated with the resonance, the Stark-forbidden and the electric quadrupole transitions from the Hel 2^1S state were observed in a plane parallel hollow cathode discharge by using laser-induced fluorescence method.A collisional-radiative model was developed to investigate effect of the collisional processes in the plasma on the fluorescences.2.The electric field distribution in the cathode dark space was determined more accurately than in our previous experiments from measured intensity ratio of the fluorescence due to the Stark forbidden to that due to the quadrupole transitions.3.Another new method was also developed to determine the electric field distribution in plasmas from measurement of only the polarization of the fluorescence which is due to both the Stark-forbidden and the quadrupole trnasitions in the dark space. The lower limit of the measurementfor the present plasma was estimated to be about 10 V/cm.4.As a future plan, a procedure will be developed to correct the effect of the charged-particle-produced microfield in rather dense plasmas, and also investigation using the triplet level system will be performed to extend this measurement.