Grazing-incidence telescope-spectrograph for space solar-imaging spectroscopy

The design of a stigmatic grazing-incidence instrument for space applicatio ns to solar-imaging spectroscopy is presented. It consists of a double tele scope and a spectrograph: Telescope I consists of a single cylindrical mirr or with parabolic section, focusing the radiation on the entrance slit of t he spectrograph in the spectral dispersion plane; telescope II consists of two cylindrical mirrors with aspherical section in a Welter configuration, focusing the radiation on the spectrograph focal plane in the direction per pendicular to the spectral dispersion plane. The spectrograph consists of a grazing-incidence spherical variable-line-spaced grating with flat-field p roperties. Telescope II is crossed with respect to the grating and telescop e I; i.e., it is mounted with its tangential planes coincident with the gra ting equatorial plane. The spectrum is acquired by a detector mounted at ne ar-normal incidence with respect to the direction of the exit beam. The spe ctral resolution is also preserved for off-axis angles. The effective colle cting area of the instrument can be preserved by adoption of a nested confi guration for telescope II without degradation of the spectral resolution. ( C) 2001 Optical Society of America.