Optical coherence techniques for plasma spectroscopy (invited)

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Abstract
A new electro-optically modulated optical solid-state (MOSS) spectrometer has been constructed for high temporal resolution measurement of the coherence of line radiation from plasmas. The instrument is an electro-optically modulated fixed delay polarization interferometer, or Fourier transform spectrometer. It has high light throughput compared with conventional grating based instruments of comparable resolving power while being compact and robust against alignment errors. By employing electro-optical path-length modulation techniques, the spectral information is transferred to the temporal frequency domain and can be obtained using a single photodetector. A wide field-of-view MOSS camera has been developed for imaging applications, while multiple-delay variants of the basic single fixed delay instrument have also been successfully tested. We discuss applications including passive Doppler spectroscopy, charge exchange recombination spectroscopy, and Zeeman and motional Stark effects. For Doppler tomographic applications, we show that such time-domain instruments have certain fundamental advantages, not least of which is a simple relationship between fringe visibility and the line integral of the intensity weighted velocity distribution function.