Sub-Doppler Double-Resonance Spectroscopy of Methane Using a Frequency Comb Probe

We report the first measurement of sub-Doppler molecular response using a frequency comb by employing as probe in optical-optical double-resonance spectroscopy. use $3.3\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ continuous wave pump and $1.67\text{ to detect transitions $2{\ensuremath{\nu}}_{3}$ $3{\ensuremath{\nu}}_{3}$ bands methane with $\ensuremath{\sim}1.7\text{ }\mathrm{MHz}$ center accuracy. These measurements provide verification accuracy theoretical predictions from highly vibrationally excited states, needed model high-temperature spectra exoplanets. Transition frequencies band show good agreement TheoReTS line list.