Comparison of infrared upconversion methods for photon-limited imaging

Abstract

Photon-limited imaging and image processing has several advantages.1 Among the advantages are ease of implementation and speed of processing. However, photon-limited imaging requires the use of detectors which can respond to single photons. Until recently photon counting has been restricted to wavelengths in the visible or ultraviolet range. Our goal is to extend photon-limited imaging techniques into the infrared region. An attractive method is to upconvert the infrared image into a visible or ultraviolet image so that a conventional photoemissive detector can be used. The upconversion efficiency need not be large because the photon-limited image is restricted to low flux levels of the order of 10−14 W. We have defined a figure of merit appropriate to passive, infrared, photon-limited imaging and have used this figure of merit to analyze three upconversion devices. These devices are an infrared quantum counter, a sum frequency generator, and an upconverting phosphor. The results of the analysis show that each upconversion method has an optimum wavelength of operation. The optimum wavelength depends on the background thermal noise from the upconversion cell and also on the upconversion efficiency. The analysis also indicates the object temperature regions in which the different devices are useful.