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

Abstract

Diffraction gratings used in ultraviolet astronomical spectrographs have been made using mechanical ruling or interference lithography. However, required performance for newly developed EUV (10-90 nm) and FUV (100-180 nm) spectrographs can benefit from groove densities, blaze angles, and low-scatter enabled with electron-beam lithography patterning and chemical etching. We report on the fabrication of custom grating prototypes developed at the Nanofabrication Laboratory at Penn State University. The gratings in development for the ESCAPE NASA Small Explorer (Univ. of Colorado/Boulder) involve writing specific patterns of curved grooves with variable line density on flat substrates. The design of the grating within the DEUCE sounding rocket payload involves writing straight grooves on a spherically curved substrate. All gratings are subsequently etched to achieve the specified blaze in the silicon. These efforts are enabling new applications in the field of astronomical UV spectroscopy.