Large format three-mirror dispersive spectrometer optics

An imaging spectrometer comprising:

• an entrance slit having a length in a cross-scan direction
• a primary mirror having a first free-form optical surface and positioned to receive optical radiation from the entrance slit and to reflect the optical radiation, the primary mirror being spaced a first distance from the entrance slit measured along a primary optical axis of the imaging spectrometer;
• a secondary mirror having a second free-form optical surface and a diffraction grating formed on the second free-form optical surface, the secondary mirror positioned to receive the optical radiation from the primary mirror, and configured to disperse the optical radiation into its spectral components to produce dispersed optical radiation, and to reflect the dispersed optical radiation, the secondary mirror being spaced from the primary mirror by a second distance measured along the primary optical axis, the second distance being approximately 0.68 of the first distance;
• and
• a tertiary mirror having a third free-form optical surface and positioned and configured to receive the dispersed optical radiation reflected from the secondary mirror and to reflect and focus the dispersed optical radiation onto an image plane coincident with the entrance slit.