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

Abstract

We report the measurement of sub-Doppler double-resonance transitions in methane using a 3.3 $\mu$m continuous wave optical parametric oscillator to pump transitions in the fundamental ${\nu }_3$ band and a 1.67 $\mu$m frequency comb to probe ladder-type transitions in the 3${\nu }_3$ 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.

References in corpus (3)

• An accurate, extensive, and practical line list of methane for the HITEMP database
• The spectrum of hot methane in astronomical objects using a comprehensive computed line list
• Exoplanet atmospheres with GIANO II. Detection of molecular absorption in the dayside spectrum of HD 102195b

Cited by in corpus (14)

• 11-μs Time-resolved, Continuous Dual-Comb Spectroscopy with Spectrally Filtered Mode-locked Frequency Combs
• Data availability and requirements relevant for the Ariel space mission and other exoplanet atmosphere applications
• Sub-Doppler optical-optical double-resonance spectroscopy using a cavity-enhanced frequency comb probe
• Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370 cm${}^{-1}$ range of methane using optical frequency comb double-resonance spectroscopy
• Polarization-dependent Intensity Ratios in Double Resonance Spectroscopy
• Sub-nominal resolution Fourier transform spectrometry with chip-based combs
• Combined frequency comb and continuous wave cavity-enhanced optical-optical double-resonance spectrometer in the 1.7 $\mu$m range
• Line positions and intensities of the ${\nu }_1$ band of ${}^{12}$CH${}_3$I using mid-infrared optical frequency comb Fourier transform spectroscopy
• Precision spectroscopy of non-thermal molecular plasmas using mid-infrared optical frequency comb Fourier transform spectroscopy
• The HITRAN2024 methane update
• Assignment of collision-induced four-level double-resonance transitions in the 3$\nu$${}_3$ $\Leftarrow$ $\nu$${}_3$ spectral region of methane
• A methane line list with sub-MHz accuracy in the 1250 to 1380 cm-1 range from optical frequency comb Fourier transform spectroscopy
• Measurement and assignment of E-symmetry states in the 6010-6110 cm${}^{-1}$ and 8940-9150 cm${}^{-1}$ ranges of methane using optical frequency comb double-resonance spectroscopy
• Theory of Lineshapes in Optical-Optical Double Resonance Spectroscopy