Optical design of the SCUBA-2 IFTS

An Imaging Fourier Transform Spectrometer (IFTS), named FTS-2, is being developed by the University of Lethbridge for use with the SCUBA-2 sub-millimeter bolometric camera on the James Clerk Maxwell Telescope (JCMT). The FTS-2 optical model was developed and optimized in Zemax by the Institut National d'Optique (INO) to maximize the FOV and efficiency over a range of spectral resolutions. The IFTS has been designed as a folded system including corner cubes in the interferometer moving mirror, and extended polynomial surfaces in the interferometer folding mirrors. The instrument design for FTS-2 is described elsewhere; here we present an analysis of the modeled performance of the IFTS in terms of achievable Field Of View (FOV), spot pattern and vignetting, at Zero Path Difference (ZPD) and for the 2 resolution modes. The predicted imaging performance is compared to that of the SCUBA-2 camera alone.