Polarized laser-induced fluorescence spectroscopy for measuring electric field distribution in plasmas

Abstract

A sensitive and reliable spectroscopic system measuring simultaneously polarized components of time-resolved laser induced fluorescence (LIF) is being developed for determining electric field distribution in transient plasmas under strong magnetic field. In this LIF method which we have already proposed, only the polarization has to be observed of a LIF due to a laser-excited forbidden transition caused by both the Stark effect and the electric quadrupole (QDP) moment in the plasmas. Temporal evolution of both the polarized LIF components is simultaneously observed using a Glan–Thompson polarizing beamsplitter with extinction ratio of 10−5 and a pair of photomultipliers with fast rise time. The polarization components observed in a hollow cathode discharge He plasma under magnetic field of 2.5 kG were successfully analyzed and electric field distribution in the sheath region was accurately estimated using this procedure. It was also shown that electric field strength was determined from the intensity ratio of the Stark and QDP components separated in the strong magnetic field. We briefly discuss the applicability of this spectroscopic system to diagnostic in the edge region of tokamak plasmas.