MAVIS: An optical design for the image slicer and spectrograph

The proposed MAVIS instrument for VLT UT4 delivers a 30 '' x 3 '' MCAO-corrected field for 370-950nm. It includes an integral-field spectroscopic mode, whereby a subsection of the field is delivered to an image slicer and spectrograph, with either 25mas or 50mas spatial sampling, and R>4000 and R>10000 modes in either the red or the blue. Three designs are being considered for the image slicer, two with all-reflective optics, and the other, presented here, derived from the existing WiFeS spectrograph and including arrays of small lenses. A spectrograph design is also presented, challenging because of the need to be close to diffraction-limited across the entire wavelength range, while maintaining high throughput, in all 4 modes and over the entire 9cm x 9cm detector.