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

美国国家航空航天局(NASA)红外望远镜设施(IRTF)的CSHELL光谱仪，建议购买一套圆形可变滤光片(CVF)。这将消除光谱中的干涉条纹图案，提供额外的波长覆盖，并阻止来自相邻梯形光栅的带外辐射。这些CVF采用楔形衬底设计，已在离散波长窄带滤光器上成功测试，但这将是此类设计首次被纳入CVF。在天文光谱仪中，CVF的干涉条纹是一个普遍存在的问题，严重限制了信噪比。CSHELL光谱中的干涉图案造成的低信噪比限制了许多关键项目的科学结果。新的滤波器将极大地提高CSHELL的信噪比性能。***

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. ***