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Immersion gratings that may realize smaller, lighter, high-resolution wide-swath imaging spectrometer for global daily tracking of atmospheric gases and other missions.
Large Gratings
Large Gratings will Give a Wider View
Daniel Wilson
The next generation of imaging spectrometers will aim to measure wide swaths of the ground or atmosphere in a single satellite orbit or aircraft flight. This increased swath width requires wide-angle optical systems, which in turn require larger gratings with increased center-to-edge height sag. Both Offner and Dyson imaging spectrometer designs are envisioned and require convex and concave gratings, respectively. MDL is currently extending e-beam fabrication techniques to allow these larger gratings to be fabricated with high precision in reasonable exposure times.
Fabrication techniques are also in development for immersion gratings on which the light is incident from within the substrate material, typically a prism made of high-refractive index glass or infrared transmissive silicon. Because the refractive index, the required grating and optical system size to achieve a given resolving reduce the light wavelength inside the substrate power or dispersion is also reduced.
Optical designs that utilize immersion gratings to realize smaller, lighter, high-resolution wide-swath imaging spectrometers are being considered for future missions that aim to measure the global distribution of atmospheric gases on a daily basis. To fabricate immersion gratings, JPL is pursuing multiple approaches, including MDL’s analog e-beam lithography process as well as binary e-beam lithography, followed by wet anisotropic silicon etching at the University of Texas at Austin through a collaboration with a group led by Professor Dan Jaffe.
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