26 February 2003 Compact high-resolution 3D imaging spectrometer for discovering oases on Mars
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Two key infrared instrument components, high resolution silicon grisms and cryogenic image slicers, are being developed at Penn State under NASA support for potential applications in future Mars missions. These new instrument components are planned to be used in a new kind of instrument called a CUBE Machine for detecting and characterizing possible organic compounds on the martian surface through spectroscopically observing martian rocks, soil, and organic matter in IR wavelengths (1-5 μm). It is a compact, robust and light-weight 3D near-IR imaging spectrometer and takes full advantage of these new instrument components to enable an order of magnitude improvement in spectral resolution and observing efficiency and also large simultaneous wavelength coverage (~1-5 μm). Due to high dispersion (n = 3.4), silicon grisms provide at least 2 times higher spectral dispersion than any commercially made grisms. These silicon grisms will be the key elements for making the instrument compact enough to fit into spacecrafts and simultaneously provide high enough spectral resolution to resolve the weak spectral features from organic materials. The reflective imaging slicers enable us to collect spectral information from the Mars surface in three dimensional form - two spatial dimensions and one spectral dimension. This unique capability obviates the need to make many scans to build up the data cube as traditional instruments such as spot scanned spectrometers, or slit scanned spectrometers, resulting in an order of magnitude increase in observing efficiency. In addition, use of the Cube Machine to produce spectral maps of a target body will result in dramatically reduced operational complexity, data processing complexity, and increased geometric fidelity of the final data. With current available large IR arrays such as 2kx2k HgCdTe arrays this new instrument will provide large simultaneous wavelength coverage at high spectral resolution. We have successfully developed silicon grisms with 1 inch in dimension and 54.7 degree in blaze angle. These grisms can provide a diffraction-limited spectral resolution of R~20,000 at 2 μm, which is already high enough for most astrobiology space mission applications. The grisms have very smooth grating facets, with typical rms roughness of ~9 nm, indicating a total integrated scattered light level less than 1% in the entire IR wavelengths to allow high precision spectroscopy. The optical design of the image slicers has been finished. The optics required to assemble a prototype image slicer is being procured.
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Jian Ge, Jian Ge, Deqing Ren, Deqing Ren, Jonathan I. Lunine, Jonathan I. Lunine, Robert H. Brown, Robert H. Brown, Roger V. Yelle, Roger V. Yelle, Laurence A. Soderblom, Laurence A. Soderblom, } "Compact high-resolution 3D imaging spectrometer for discovering oases on Mars", Proc. SPIE 4859, Instruments, Methods, and Missions for Astrobiology V, (26 February 2003); doi: 10.1117/12.457334; https://doi.org/10.1117/12.457334

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