Infrared heterodyne spectroscopy is an extremely useful tool for Doppler-limited studies of atomic and molecular lines in diverse astrophysical regions. The current state of the art is reviewed, and the analysis of CO2 lines in the atmosphere of Mars is outlined. Doppler-limited observations have enabled the discovery of natural laser emis-sion in the mesosphere of Mars and the discovery of failure of local ther-modynamic equilibrium near the surface of Mars.
Michael J. Mumma,
"Infrared Heterodyne Spectroscopy," Optical Engineering 21(2), 212313 (1 April 1982). https://doi.org/10.1117/12.7972901