An infrared upconverter for astronomical imaging

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Abstract
An imaging upconverter has been constructed which is suitable for use in the study of the thermal 10‐μm radiation from astronomical sources. The infrared radiation is converted to visible radiation by mixing in a 1‐cm‐long proustite crystal. The phase‐matched 2‐cm−1 bandpass is tunable from 9 to 11 μm. The conversion efficiency is 2×10−7, and the field of view of 40 arc seconds on the sky contains several hundred picture elements, approximately diffraction‐limited resolution in a large telescope. The instrument has been used in studies of the sun, moon, Mercury, and VY Canis Majoris.