Abstract: Disclosed herein are spectral imaging systems having an internally folded prism, which can have four different refracting surfaces. A first angle defines the spatial relationship between the first and second refracting surfaces. The first angle can have a range between 45-95 degrees. In some embodiments, the first angle can be 70 degrees. The spatial relationship of the third and fourth refracting surfaces can be defined by a second angle, which can be the same as the first angle. Finally, the spatial relationship of the second and third refracting surfaces can be defined by a third angle, which can have a range between 90-145 degrees. The prism index of refraction, the first, second, and third angles are selected such that TIR is achieved at two of the refracting surfaces. Additionally, these prism parameters are selected such that a 180 degrees fold of the optical path is achieved entirely within the prism.

Abstract: A device for the spectral dispersion of light suitable for use in a spectrographic mode with arrays of solid state photo-detectors. Light from an entrance aperture passes through a dispersing prism with two curved, refracting surfaces both operating near their aplanatic conjugates. After being reflected by a concave mirror located behind the prism, light returns through the prism in the opposite direction, the refractions at each face again being nearly aplanatic. Spectrally dispersed images of the entrance aperture are formed on a plane well separated from the entrance aperture and nearly normal to the incident light rays. Good image quality is maintained over a broad range of operating wavelengths simultaneously, allowing large spectral intervals to be surveyed without moving any of the elements of the system.