A compact wide-spectrum imaging spectrometer using freeform surface

This paper presents a compact imaging spectrometer covering visible–near-infrared (VNIR) and shortwave-infrared (SWIR) spectrum with a large field-of-view (FOV). The design is composed of a curved prism for dispersing beam and two freeform mirrors mainly for balancing off-axis high-order aberrations. In this study, the FOV with a much longer slit of 50 mm from 400 nm to 2500 nm is constructed, three types of different designs using spherical, aspherical, and freeform surfaces are compared under the same specifications. Results show that the combination of freeform surfaces and prism can effectively improve the imaging quality of off-axis fields and compress the volume. The volume of the design based on freeform surface is reduced by 0.55 times than the corresponding spherical design.