Selectable magnification reflective triplet (SMaRT) imaging spectrometer

The optical form of an imaging spectrometer for an airborne or space-borne EO/IR payload is often selected based on evaluation of the performance and size, weight, power, and cost (SWaP-C) of candidate spectrometer forms, the most commonly selected being Offner-Chrisp and Dyson spectrometers. Although these trades consider spectrometer metrics, the implications to the complexity and performance of the overall, higher-level system including other EO/IR sensors, are not always considered and may be far from equivalent. The Selectable Magnification Reflective Triplet (SMaRT) spectrometer is presented (shown in Figure 1) which offers greater system flexibility and potentially reduced complexity of the higher-level system. The SMaRT is a single-pass, unfolded form of the reflective triplet (RT) spectrometer. It has an RT collimator with real exit pupil at a dispersive element followed by a separate RT imager and focal plane –the focal lengths for the collimator and imager portions being independently selected. This allows an EO/IR payload with a SMaRT spectrometer and other EO/IR sensor(s) to potentially share imaging optics at an f-number selected for optimal performance of one or more of the other EO/IR sensors (e.g., optimized to provide high resolution context imagery), while separately selecting the f-number of the imager portion of the SMaRT to achieve the desired irradiance and resolution at the spectrometer focal plane. A system level trade is presented evaluating system complexity for comparably performing systems with a SMaRT or Offner-Chrisp spectrometer and high resolution context camera.