Heterodyne detection in the infrared and optical is a useful technique for systems applications such as spectroscopy and radiometry. The use of heterodyne detection techniques has been demonstrated in many regions of the electromagnetic spectrum including the radiowave, microwave, infrared, and optical. Heterodyne detection offers the advantages of high sensitivity, frequency selectivity, and strong directivity.
Heterodyne radiometers using lasers as local oscillators are useful for detecting weak radiation signals which have narrow spectral widths. This detection technique is very useful for detecting thermal and non-thermal radiation from planetary atmospheres, including the earth, and from gaseous clouds surrounding infrared radiating stars.
There are two types of detectors that are available for infrared heterodyne detection. These devices are capable of attaining bandwidths in the 500 to 2000 MHz range and noise equivalent powers of less than 6.2 x 10('20)W/Hz. The detectors are capable of attaining shot-noise-limited behavior and high sensitivities when operated in the heterodyne mode.
This document contains an analytical model that is capable of predicting the performance of the heterodyne detectors. In addition, the techniques for fabricating and characterizing these detectors are described and experimental results are presented which are typical of the operating characteristics of these devices.
