The PRISM spectrometer incorporates several innovations including a fast and uniform design with a total internal reflection fold, a polarization-insensitive shaped groove concave grating, a black-Si slit for uniformity and stray light reduction, and a fast, wide angle two-mirror telescope. The spectrometer is of the Dyson design form which permits a high throughput (F/1.8) and also provides low angles of incidence for controlling polarization variation. All transmissive elements are made of fused silica with a high-quality broadband anti-reflection coating.

Ray trace of the telescope/spectrometer system in the direction of dispersion.

Photograph of the concave diffraction grating and measured groove profile of same. The blazed first order can be seen displaced from the zero order observed most strongly on the unexposed outside ring.

SWIR radiometer design