We present an ultrahigh-resolution saturation spectrometer based on a line-tunable carbon monoxide laser near 60 THz (λ = 5 µm). A spectral resolution of 14 kHz (Δν/ν = 2.3 × 10-10) for CO fundamental-band transitions was achieved, which improves on earlier results by one order of magnitude. A frequency-locking scheme using tunable microwave sidebands provides tunability and absolute frequency control of the CO laser on the kilohertz. Transit-time broadening and pressure broadening of the observed transitions are significantly reduced by use of expanded laser beams in a 24-m absorption cell at pressures down to 0.0 1Pa. The new spectrometer is suitable for the study of saturation line shapes and the development of a new generation of frequency standards in the 60-THz region.
© 2001 Optical Society of America
P. Palm, D. Hanke, W. Urban, and M. Mürtz, "Ultrahigh-resolution spectrometer for the 5-µm wavelength region," Opt. Lett. 26, 641-643 (2001)