Modulated optical solid-state spectrometer applications in plasma diagnostics

Abstract

A new electro-optically modulated optical solid-state (MOSS) interferometer has been constructed for the measurement of the low order spectral moments of line emission from optically thin radiant media. The instrument, which is based on the principle of the Fourier transform spectrometer, is rugged, compact, and inexpensive and offers a number of advantages over conventional grating based spectrometers. Most importantly, by employing electro-optical path-length modulation techniques, the spectral information is obtained using a single photomultiplier tube. Specifically, the zeroth moment (brightness) is given by the average signal level, the first moment (shift) by the modulation phase and the second moment (line width) by the modulation amplitude. In applications such as Zeeman spectroscopy and motional Stark effect (MSE), polarization modulation can be used to effect a modulation of the center frequency and/or coherence of the light which is then measured by the MOSS spectrometer. This article describes a number of applications, including Doppler and charge exchange recombination spectroscopy and polarization spectroscopy (Zeeman and MSE) for which the MOSS spectrometer is an inexpensive and powerful alternative to multichannel grating spectrometers.