Replication of a holographic ion-etched spherical blazed grating for use at extremeultraviolet wavelengths: efficiency

Using synchrotron radiation, we have measured the efficiency at an angle of incidence of 10(degree) of a holographic ion-etched spherical blazed grating and three of its fourth-generation replicas. The measured efficiency profile of replicas 1 and 3 prior to multilayer coating oscillated from thin-film interference produced by the replicasʹ Al/Al2O3/SiO2 structure. A Mo2C/Si multilayer coating was applied to the master grating and replicas 1 and 2. After coating, the maximum grating efficiency occurred in the -2nd order and the maximum values were 12.4% at 143.8 (ANGSTROM) for the master and 11.6% at 145.2 (ANGSTROM) for replicas 1 and 2. On the basis of measurements obtained after coating, the derived groove efficiency was 22.2% for the master, 19.4% for replica 1, and 19.3% for replica 2. The groove efficiency of the uncoated replica 3 was 24.3% at 142.5 (ANGSTROM). We find that the replicas are reasonably faithful copies of the ion-etched master, and models based on measured atomic force microscope groove profiles are in general agreement with measured results. However, subtle issues remain regarding the widths of the peak order profile and the location of its maximum wavelength.