High-sensitivity infrared heterodyne radiometer using a tunable-diode-laser local oscillator

A blackbody heterodyne radiometer using a widely tunable PbSnSe-diode laser as the local oscillator (LO) achieved signal-to-noise performance that was an order of magnitude better than previously reported and only a factor of 2.5 below that obtained with a CO(2)-laser LO. The diode laser system performance was within a factor of 6 of an ideal radiometer. High-resolution blackbody heterodyne absorption spectra of ethylene at 10.6 microm were obtained with a 0.4-sec post-detection integration time by tuning the diode LO in a closed-cycle cryogenic cooler.