Recent advances in blazed grating fabrication by electron-beam lithography

Convex and concave diffraction gratings are required for concentric imaging spectrometer forms. Direct-write electron-beam lithography has proven to be an effective method for fabricating high-efficiency blazed gratings on non-flat substrates. Recently fabricated convex gratings have demonstrated relative efficiency greater than 90%, diffuse scatter and ghosts less than 5x10-4 of the main diffraction order, and zeroth-order wavefront error less than 1/4-wave at 633 nm. Such gratings can be fabricated on JPL’s JEOL JBX-9300FS electron-beam lithography system with a writing speed of approximately 1 to 2 cm2 per hour. The technique was recently used to fabricate flight-qualified gratings for the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument that is scheduled to fly on the NASA Mars Reconnaissance Orbiter in 2005.