Frequency-comb-assisted precision laser spectroscopy of CHF3 around 8.6 μm

We report a high-precision spectroscopic study of room-temperature trifluoromethane around 8.6 μm, using a CW quantum cascade laser phase-locked to a mid-infrared optical frequency comb. This latter is generated by a nonlinear down-conversion process starting from a dual-branch Er:fiber laser and is stabilized against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several transitions falling in the υ5 vibrational band are recorded with a frequency resolution of 20 kHz. Due to the very dense spectra, a special multiple-line fitting code, involving a Voigt profile, is developed for data analysis. The combination of the adopted experimental approach and survey procedure leads to fractional accuracy levels in the determination of line center frequencies, down to 2 × 10(-10). Line intensity factors, pressure broadening, and shifting parameters are also provided.