AAS 201st Meeting, January, 2003
Session 82. Planning for Future Missions: Radio to X-Ray
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[82.14] A QVD Detector for Focal Plane Hyperspectral Imaging in Astronomy

K. S. Wood (NRL), A. M. Gulian (PAF), G. G. Fritz (Praxis, Inc.), D. VanVechten (ONR)

We present the latest results on the development of a new detector, called ``QVD'' for single photons, being developed by NRL under DoD and NASA sponsorship. In this approach, incoming photons are absorbed and thermalized; the resulting elevation of temperature is detected as a thermoelectric voltage generated because of the resulting temperature differential from the absorption site to a reference at the baseline temperature. Heat (Q) is converted to voltage (V) and digitized in the readout (D). The design exploits the high value of the thermoelectric, or Seebeck, coefficient that some metals (so called Kondo metals) have at cryogenic temperatures. The best-known candidates are lanthanum-cerium hexaborides, with the Seebeck coefficient as high as 100 \muV/K at ~1 K temperatures reported in bulk crystals. Bulk crystals can be used in some modifications of the QVD detectors, but other crystalline modifications such as thin films or whiskers can yield better results. Thin films are most promising from the point of view of existing electronic device fabrication technologies. Thus we focus on developing thin films of hexaborides. We have currently reached S ~7 \muV/K. Work is in progress to improve films. We hope to get one order of magnitude improvement in the near future. Then, about 1 eV energy resolution is predicted for 6 keV photons and ~0.1 eV resolution for UV photons. A major feature of thermoelectric detectors is high speed (short pulse duration, ~tens of nanoseconds), already demonstrated with prototypes. Counting rates of MHz are possible for X-ray detecting designs and even higher rates for UV-detecting designs. The parameters of the absorber (dimensions and materials) can be chosen to achieve high quantum efficiency. Simplicity of the detector layout facilitates array construction for hyperspectral imaging.

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