Grazing-incidence spectrograph.

A novel compact spectrograph, based on double diffraction by a strip-shaped grating at a grazing angle combined with a tuning mirror, is theoretically discussed. In this configuration the emerging light illuminates a large number of grooves, leading to high spectral resolution. It is shown that with large f-number optics, using a detector array, one may obtain high resolution in spite of the compact spectrograph structure. At grazing incidence the transmission and dispersion of the spectrograph depend strongly on wavelength. The grating's low efficiency and the large f-number may be compensated for by an efficient data acquisition, which may be attained with a detector array. An advantage of the geometry is that most of the original beam may be obtained as a collimated output through the zero-order reflection from the fixed grating.