CONVEX GRATING TYPES FOR CONCENTRIC IMAGING SPECTROMETERS

The properties of convex gratings fabricated by electron-beam lithogra phy are investigated. Three grating types are shown. The first is a si ngle-panel, true blazed grating in which the blaze angle stays constan t relative to the local surface normal. This grating provides high pea k efficiencies of approximately 88% in the first order and 85% in the second order. The second grating has two concentric panels, with each panel blazed at a different angle. This type permits flexibility in ma tching the grating response to a desired form. The third type has a gr oove shape that departs from the sawtooth blazed profile to increase t he second-order bandwidth. All these types are difficult or impossible to produce with conventional techniques. The gratings compare favorab ly with conventional (holographic and ruled) types in terms of efficie ncy and scatter. Simple scalar models are shown to predict the wavelen gth response accurately. These gratings allow the optical designer to realize fully the considerable advantages of concentric spectrometer f orms. (C) 1998 Optical Society of America OCIS codes: 050.1940, 050.19 50, 050.2770, 120.6200, 220.4000.