We report a source of tunable laser radiation for high-precision molecular spectroscopy in the 2.6– 4.1-µm spectral region. Laser light from a CO overtone laser is mixed with microwaves, generating tunable sidebands of ~1 mW of power. We achieve very high absolute frequency accuracy by frequency-offset locking the CO laser to a CO<sub>2</sub> laser secondary frequency standard. The uncertainty of the laser frequency is less than 30 kHz (Δν/ν=3×10<sup>-10</sup>) , and the laser linewidth is of the order of 100 kHz. This tunable and ultrastable laser system is suitable for very accurate molecular spectroscopy and metrology in a most interesting wavelength region. We demonstrate an application of the system to saturated-absorption spectroscopy of a rovibrational transition of carbonyl sulfide.
© 1998 Optical Society of America
M. Mürtz, B. Frech, P. Palm, R. Lotze, and W. Urban, "Tunable carbon monoxide overtone laser sideband system for precision spectroscopy from 2.6 to 4.1 µm," Opt. Lett. 23, 58-60 (1998)