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We report a modification of the AT&T Bell Laboratories 6m toroidal grating monochromator at the National Synchrotron Light Source at Brookhaven National Laboratory which provides greatly improved resolution at midrange without the use of a movable exit slit. This modification is based on detailed ray tracing calculation, using the precedures developed by Haber, Howells, and McKinney and Howells, modified to include the holographic correction terms to the focusing equations. To maintain the optimum resolution requires an exit slit assembly movable over a distance of ∼20 cm. However, we show that an additional fixed slit 16.8 cm closer to the grating than the standard exit slit position gives near optimum resolution in the range 70–140 eV for the 2400 line/mm grating. Resolution measurements, using the Fermi cut‐off of various metals, confirm that the full width at half maximum (FWHM) can be kept below 100 meV for photon energies from 70 to 140 eV. Further improvement (perhaps to as low as 60 meV, FWHM) can be obtained by masking the width of the grating. The modified instrument has been successfully used in a number of studies in the far‐ultraviolet and soft x‐ray regions.


AIP Conference Proceedings 215: X-Ray and Inner-Shell Processes, Knoxville, TN, 1990, edited by T. A. Carlson, M. O. Krause, and S. T. Manson (AIP, New York, 1990), p. 259 – 269.

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