The X-ray ultraviolet imager for the orbiting solar laboratory

A normal incidence multimirror telescope, the X-ray Ultraviolet Imager, for high resolution imaging of the solar atmosphere in the soft X-ray/XUV region, is being developed as part of the scientific payload of the NASA Orbiting Solar Laboratory. The X-ray Ultraviolet Imager is formed by two units: a high resolution telescope (0.25 arcsec pixel size and 8×8 arcmin2 field of view) and a wide field one (2.3 arcsec pixel size and 5×5 solar radii2 field of view). The two systems complement each other and allow a full coverage of solar features from the small scale (200 km on the sun) to the global phenomena. Each system consists of 8 channels with multilayer mirrors, imaging at different wavelengths. In each channel the mirror coating is optimized to select a narrow spectroscopic window corresponding to an intense line in the region 40-400 A˚. In order to provide imaging and temperature diagnostics from the chromosphere to the upper corona, 8 wavelengths are chosen to cover the broad temperature range from 105 to 107 K. Four images, two high resolution and two full disk ones, are simultaneously obtained by the X-ray Ultraviolet Imager, at a cadence which in flares can be of 0.4-1 s.