Optical Design for the 5-28μm NGST MIRI spectroscopy channel (MIRI-S)

MIRI, the mid-IR instrument for NGST is being provided by a collaboration between a consortium of European institutes, ESA, NASA, JPL and US scientists, with the Europeans responsible for the optics module. The instrument will provide diffraction limited imaging and spectroscopic capability over the 5-28μm region with unprecedented sensitivity. In this paper we describe the current optical design of the medium resolution spectroscopy channel (MIRI-S). This uses a novel arrangement of dichroics, image slicers and spectrometers to optimise the division of a limited number of detector pixels between spatial and spectral information whilst working within the tight mass and volume constraints imposed by a space mission. We also present our design for reflective image slicers that are adapted properly for diffraction limited performance to provide a high throughput over the full wavelength range of the instrument.