A New Circular Variable Filter Design for the NASA IRTF CSHELL Spectrograph

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ABSTRACT AST-9420506 GREENE, Thomas The PI proposes to purchase a set of circular variable filters (CVFs) for the CSHELL spectrograph of the NASA Infrared Telescope Facility (IRTF). These will eliminate interference fringing patterns in spectra, provide additional wavelength coverage, and reject out-of-band radiation from adjacent orders of the echelle grating. These CVFs incorporate a wedged substrate design which has been successfully tested on discrete-wavelength narrow-band filters, but this will be the first time such a design has been incorporated into a CVF. Interference fringing of CVFs is a common problem which seriously limits signal-to-noise in astronomical spectrographs. Low signal-to-noise caused by interference patterns in CSHELL spectra has limited the scientific results of many key projects. The new filters should greatly improve the signal-to-noise performance of CSHELL. ***