The Evaluation of Photoelectrochemically Etched Gratings in GaAs

Abstract

The GSFC Diffraction Grating Evaluation Facility has recently been used to evaluate several sets of echelle gratings in crystalline GaAs fabricated at EIC Laboratories under a small business innovative research contract. New technology echelle gratings will be required to achieve science goals for future space missions such as Space Telescope Imaging Spectrograph. The amount of scattered light in the plane of dispersion of these gratings was measured for orders on blaze. Also, the distribution of energy into the gratings’ zero orders and orders around blaze was measured for determinations of relative groove efficiency and blaze angle. Although substrate quality would not always permit quantitative evaluation of image quality, images were examined qualitatively to locate problem areas in the grating fabrication process and to assess progress in the technology of photoelectrochemically etched gratings. Preliminary results indicate that the GaAs gratings are obviously blazed at or near angles predicted by theoretical considerations relating to crystallography and to the measured stoichiometry during the photoelectrochemical etching process.