Efficiency measurements of reflection gratings in the 100-300-A band

Zero-order and first-order efficiencies of plane diffraction grazings over the 100-300-A band have been measured using the NRL beamline facility at the National Synchrotron Light Source. Measurements were taken at grating angles of 5, 10, and 15 deg, and the incident radiation was polarized primarily in the transverse magnetic mode. Four (three laminar, one blazed) of the gratings were ion etched in high quality quartz blanks, overcoated with 200 A of gold. A fifth (blazed) grating was ruled in gold. The line densities are 1000, 2000, and 3600 grooves/mm for those with laminar profiles. Both blazed gratings have a blaze angle of 8 deg and line densities of 3600 grooves/mm. Measured first-order efficiencies up to 15 percent were obtained for the laminar gratings and up to 8 percent was obtained for the ion-etched blazed grating. Much lower efficiencies (not greater than 2 percent) were measured for the ruled grating. A computer program was written to calculate grating efficiencies using a full electromagnetic model. Measured efficiencies of the ion-etched gratings agree well with predicted values, but the measured first-order efficiency of the ruled grating is much lower than predicted.