Infrared to visible parametric upconversion.
Experiments have been performed to evaluate the use of parametric laser image upconversion in proustite to convert 10.6-microm illuminated objects into visible images. The experiments evaluated the key parameters, and the results were compared to the theory. A diffuse scatterplate was illuminated with radiation from a CO(2) laser operating at 10.6 microm. The upconversion efficiency, angle of acceptance, tunability, bandwidth, and image resolution of the system were measured. The results were found to be in agreement with theory. The upconversion efficiency of the 1-cm-long mixer used was 6 x 10(-6) for a local oscillator power density of 44 W/cm(2). The half-power angle of acceptance for a 1-cm-long mixer was found to be 8 degrees . Different frequency modes of the CO(2) laser were identifiable by first tuning the laser and then following with the mixer. The tuning constant near 10.6 microm was measured to be 0.25 microm per degree of optic axis rotation. The acceptance bandwidth of the 1-cm-long proustite mixer was found to be 0.015 microm. In the imaging experiments, a diffuse reflecting, 100% contrast bar chart sequence was used to measure resolution, which, limited by transverse multimode local oscillator beam divergence, was found to be 20 mrad/cycle for a 25% depth of modulation in the upconverted signal. A source of internal parametric light was observed in the proustite mixer. Measurements of the light level, its temperature dependence, its phase matching dependence, a comparison with upconverted external blackbody radiation, and second-order parametric effects have been made. The light appears to be upconverted thermal radiation from within the proustite mixer.
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