Construction of a flat-field grazing incidence spectrograph

The report describes a spectrograph incorporating a concave diffraction grating designed for the wavelength range from 50 to 200 angstroms, focusing on the performance of the spectrograph and the adjustment of the spectroscope for it. A toroidal mirror is employed as a front-side optical system to produce an image of the light source. Its design is also discussed. In addition, the report presents a method for approximate determination of the wavelength from a spectrogram. Though smaller in dispersion and lower in resolution as compared to the Rowland type grazing incidence spectroscope, the flat-field grazing incidence spectroscope proposed here, when combined with a one-dimensional and a two-dimensional light detector, provides a useful tool for recording the temporal changes in various light sources, because the image-formation plane in the spectroscope is flat. A toroidal diffraction grating or a front-side optical system incorporating a toroidal mirror is necessary to record spatial changes. The toroidal mirror may be adopted in most cases because the toroidal diffraction grating is not widely available. (N.K.)