Fabrication of custom astronomical gratings for the extreme and far ultraviolet bandpasses

Diffraction gratings used in ultraviolet astronomical spectrographs have traditionally been made using mechanical ruling or interference lithography. However, necessary performance for newly developed extreme (EUV: 10-90 nm) and far-ultraviolet (FUV: 90-180 nm) spectrographs require groove densities, blaze angles, and low-scatter enabled with electron-beam lithography patterning and chemical etching. We report on the fabrication of a custom grating prototype developed at the Nanofabrication Laboratory at Penn State University. The gratings in development for the ESCAPE NASA Small Explorer mission (Univ. of Colorado/Boulder) involve writing specific patterns of curved grooves with variable line density on flat substrates. All gratings are subsequently etched to achieve the specified blaze in the silicon. These efforts are opening the way to new applications in the field of astronomical UV spectroscopy.