Efficiency and long-term stability of a multilayer-coated, ion-etched blazed holographic grating in the 125-133-Å wavelength region.

The efficiency of an ion-etched blazed holographic grating was measured by the use of synchrotron radiation in the 125-133-Å wavelength range and at near-normal incidence. The grating had a Mo-Si multilayer interference coating that resulted in a peak normal-incidence efficiency of 13% in the second grating order and at a wavelength of 128 Å. This is the highest efficiency obtained to date from a multilayer-coated grating in this wavelength region and at normal incidence. These measurements are compared with similar measurements performed on the same grating 4.5 years later. Over this time the peak grating efficiency decreased from 13% to 8%, and this result is attributed to the decrease in the reflectance of the multilayer coating from 55% to 42%. Oxidation and contamination of the multilayer with carbon appear to be the causes of these losses. The groove efficiency of the grating substrate in the second order is 23%.