Optical design of the FUEGOS high-resolution multiple fiber spectrograph

This paper describes the feasibility design of a high resolution multiple object fiber spectrograph. High resolution is obtained without cross dispersion with large 305 mm ruled length gratings and the use of the fiber link as an image slicer. The grating has a high groove density to provide a free spectral range larger than the CCD detector. The use of microlenses as focal converter at the slit has several implications on the design of the spectrograph. Unlike single object spectrographs, the presence of a significant telecentric slit field, 6 degrees long, makes the standard parabolic collimator inappropriate. A catadioptric collimator is used instead in double pass to image the intermediary spectrum sideways of the slit. The use of the white pupil and the good image quality of the collimator permit various camera options. The one foreseen is a f/1.25 finite conjugate catadioptric camera with a (2048) 2 24 micrometers pixel detector.