Application of the Liquid-Crystal-Based Tunable Lyot Filter to the Optical Emission Imaging Plasma Spectrometry

抄録

An imaging spectrometry of plasmas using a tunable Lyot filter for the visible range (400-720 nm) is proposed. The typical passband and transmittance of the filter in the present study are 7 nm FWHM and 12 % at 550 nm. An optical system has been developed for a MAP-II divertor/edge plasma simulator. The line contamination was defined as the contributions of the adjacent lines in the passband of the filter and of the lines in the leak-band which were observed at longer than 548 nm at a specific wavelength setting below 455 nm. We found that it is desirable to use a low-pass or band-pass filter to cut leak-bands, and that the He I lines of 447, 471, 492, 501 and 587 nm can be used for pure He plasma. Based on the CR model, the parameter range where these line ratios were applicable in our discharge condition of 12 mTorr was evaluated for the electron temperature of T_e < 20 eV and the electron density of 10¹¹ < n_e < 10¹⁴ cm^-3.