Spherical-grating monochromator with a variable-line-spaced grating for synchrotron radiation

An optical design for spherical-grating monochromators for application to s ynchrotron radiation is presented. High spectral and spatial performance is obtained with a spherical variable-line-spaced grating coupled to a spheri cal mirror with its tangential plane coincident with the grating's equatori al plane. The monochromator works without an entrance slit in an off-Rowlan d configuration with a fixed entrance arm and demagnification on the exit s lit. The law for groove-space variation of the grating compensates for the main spectral aberrations; spectral focusing in an extended energy range is ensured by a slight change in the exit arm with translations of the order of a few tens of millimeters. The inclusion of a spherical mirror ensures f ocusing on a plane perpendicular to the plane of spectral dispersion. The u ltimate resolution is limited by the slope errors of a single spherical sur face. The layout is applied to the design of a high-resolution monochromato r for the 1000-250-eV region. (C) 2000 Optical Society of America. OCIS cod es: 340.6720, 050.1950, 120.4570, 120.6200.