Sub-Doppler Double-Resonance Spectroscopy of Methane Using a Frequency Comb Probe
Aleksandra Foltynowicz, Lucile Rutkowski, Isak Silander, Alexandra C. Johansson, Vinicius Silva de Oliveira, Ove Axner, Grzegorz Soboń, Tadeusz Martynkien, Paweł Mergo, Kevin K. Lehmann
Abstract
We report the first measurement of sub-Doppler molecular response using a frequency comb by employing the comb as a probe in optical-optical double-resonance spectroscopy. We use a $3.3\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ continuous wave pump and a $1.67\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ comb probe to detect sub-Doppler transitions to the $2{\ensuremath{\nu}}_{3}$ and $3{\ensuremath{\nu}}_{3}$ bands of methane with $\ensuremath{\sim}1.7\text{ }\text{ }\mathrm{MHz}$ center frequency accuracy. These measurements provide the first verification of the accuracy of theoretical predictions from highly vibrationally excited states, needed to model the high-temperature spectra of exoplanets. Transition frequencies to the $3{\ensuremath{\nu}}_{3}$ band show good agreement with the TheoReTS line list.