HIGH-SENSITIVITY MIDINFRARED HETERODYNE SPECTROMETER WITH A TUNABLE DIODE-LASER AS A LOCAL OSCILLATOR

A new mid-IR heterodyne spectrometer, which is intended to be applied for atmospheric and astrophysical studies, is presented. The spectrome ter uses a frequency-stabilized tunable diode laser as a local oscilla tor. Owing to the low output power of available single-mode diode lase rs, a newly developed confocal-ring resonator, the diplexer, is used t o superimpose the source signal efficiently with that of the local osc illator. Additionally, the diplexer serves as an optical filter that e stablishes controlled optical feedback between the laser diode and the detector, which allows stable laser operation with linewidths of the order of 1 MHz. The heterodyne signal from the HgCdTe detector is anal yzed by means of a 1.4-GHz acousto-optical spectrometer. With this set up we find system temperatures as low as 4400 K (double sideband), tha t is, approximately a factor of 6 of the quantum Limit. (C) 1998 Optic al Society of America.