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 method for measuring spectral characteristics includes capturing spectral-spatial data that includes radiance measurements over spectrally flat, highly emissive surface portions of a sample material and heater at least two different heater temperatures for transmissive and/or emissive configurations. Temperatures of the sample material and heater are determined at the different heater temperatures for each configuration using, in each instance, radiance measurements taken after the temperatures of the heater and sample material have both stabilized. The transmissivity of the sample material is determined using the temperatures determined in the transmissive configuration and spectral-spatial data collected at selected points of interest over the sample material. The emissivity of the sample material is determined using the temperatures determined in the emissive configuration, the spectral-spatial data collected at selected points of interest over the sample material, and the transmissivity.

Abstract: A method for measuring spectral characteristics includes capturing spectral-spatial data that includes radiance measurements over spectrally flat, highly emissive surface portions of a sample material and heater at least two different heater temperatures for transmissive and/or emissive configurations. Temperatures of the sample material and heater are determined at the different heater temperatures for each configuration using, in each instance, radiance measurements taken after the temperatures of the heater and sample material have both stabilized. The transmissivity of the sample material is determined using the temperatures determined in the transmissive configuration and spectral-spatial data collected at selected points of interest over the sample material. The emissivity of the sample material is determined using the temperatures determined in the emissive configuration, the spectral-spatial data collected at selected points of interest over the sample material, and the transmissivity.

Abstract: A spectrometer apparatus includes a refractor element, a slit, a detector, a diffraction grating, and a corrector lens. The refractor element includes a rear surface and a front surface. The slit provides an optical path to the rear surface of the refractor element, and is configured to transmit an image incident thereupon along the optical path. The detector is positioned facing the rear surface of the refractor element. The diffraction grating faces the front surface of the refractor element, and is configured to spectrally disperse and reimage the image of the slit toward the front surface of the refractor element. The corrector lens is positioned between the refractor element and the diffraction grating such that the image is provided to the detector corrected for a spherical aberration caused by a separation distance between the detector and the rear surface of the refractor element.

Abstract: A spectrometer apparatus includes a refractor element, a slit, a detector, a diffraction grating, and a corrector lens. The refractor element includes a rear surface and a front surface. The slit provides an optical path to the rear surface of the refractor element, and is configured to transmit an image incident thereupon along the optical path. The detector is positioned facing the rear surface of the refractor element. The diffraction grating faces the front surface of the refractor element, and is configured to spectrally disperse and reimage the image of the slit toward the front surface of the refractor element. The corrector lens is positioned between the refractor element and the diffraction grating such that the image is provided to the detector corrected for a spherical aberration caused by a separation distance between the detector and the rear surface of the refractor element.

Abstract: An all reflective telescope system generally includes two spherical mirrors, one mild aspheric mirror and one aspheric mirror all centered about a common telescope axis and imaging on a focal surface for easy manufacture, very long focal length, wide field of view, high resolution, compact volume and low weight particularly well suited for space observations, and in a detailed form includes a sectional concave hyberboloidal primary mirror, a circular mild convex ellipsoidal secondary mirror, a sectional concave spherical tertiary mirror and a sectional convex spherical quaternary mirror for focusing an extended distant object onto a concave cylindrical focal surface having a linear array of charge coupled detectors for high resolution imagery, the telescope having high performance operation near diffraction limits and operating at detector resolution limits.