Rapid Scan Spectrometers for the Diagnostics of Transient Plasmas

An observation that a symmetrical configuration of off-axis paraboloidal mirrors produces an excellent image of an extended slit, while an unsymmetrical configuration produces poor images, has led to a modification of the original Sandia rapid scan spectrometer and to the design of a new wide range, rapid scan spectrometer. The new instrument employs a high speed rotating mirror in a Littrow arrangement to obtain a spectral scan speed double that of the original spectrometer; e.g., with a 600-lines/mm grating, a spectral scan speed of ~410 A/microsec is obtained at 1000 rps. Techniques for obtaining an accurate calibration of the spectral scan speed are described, and some examples of spectra which were recorded from a xenon and a hydrogen plasma are shown.