We report the measurement of sub-Doppler double-resonance transitions in methane using a 3.3 μm continuous wave optical parametric oscillator to pump transitions in the fundamental ν3 band and a 1.67 μm frequency comb to probe ladder-type transitions in the 3ν3 band over 200 cm−1 of bandwidth. We detected 36 ladder-type resonances for 9 pumped transitions with average center frequency accuracy of 1.7 MHz, limited by the pump frequency stability. The lines are assigned using the TheoReTS line list, and the intensity ratios for different relative pump/probe polarizations. This method provides accurate assignment of highly excited energy levels that cannot be done using high temperature spectra.
@article{arxiv.2001.08781,
title = {Sub-Doppler Double-Resonance Spectroscopy of Methane Using a Frequency Comb Probe},
author = {Aleksandra Foltynowicz and Lucile Rutkowski and Isak Silander and Alexandra C. Johansson and Vinicius Silva de Oliveira and Ove Axner and Grzegorz Soboń and Tadeusz Martynkien and Paweł Mergo and Kevin K. Lehmann},
journal= {arXiv preprint arXiv:2001.08781},
year = {2023}
}