COMPARISON OF THE CALCULATED AND THE MEASURED EFFICIENCIES OF A NORMAL-INCIDENCE GRATING IN THE 125-225-ANGSTROM WAVELENGTH RANGE

The efficiency of a diffraction grating was measured near normal incid ence in the 125-225-Angstrom wavelength range with synchrotron radiati on. The grating pattern had 2400 grooves/mm and was recorded on a conc ave fused-silica blank by a holographic technique. The grooves were sh aped by ion-beam etching to provide a facet with a blaze angle of 2.5 degrees as determined by atomic force microscopy. Because of the chara cteristics of the etching process the groove profile was approximately triangular, with the other facet inclined at an angle of 5.5 degrees to the surface. The measured efficiency was compared with the efficien cy calculated by a computer program, small enough to run on a personal computer, that solved the periodic boundary-value problem correspondi ng to electromagnetic radiation incident on a diffraction grating with finite conductivity. The calculation was based on the nominal groove profile that was determined by atomic force microscopy. The measured a nd the calculated efficiencies were in good agreement. This investigat ion indicates that the diffraction efficiency of a normal-incidence gr ating can be calculated in the soft-x-ray region with a personal compu ter. (C) 1997 Optical Society of America.