Sub-Doppler optical-optical double-resonance spectroscopy using a cavity-enhanced frequency comb probe

Abstract

Accurate parameters of molecular hot-band transitions, i.e., those starting from vibrationally excited levels, are needed to accurately model high-temperature spectra in astrophysics and combustion, yet laboratory spectra measured at high temperatures are often unresolved and difficult to assign. Optical-optical double-resonance (OODR) spectroscopy allows the measurement and assignment of individual hot-band transitions from selectively pumped energy levels without the need to heat the sample. However, previous demonstrations lacked either sufficient resolution, spectral coverage, absorption sensitivity, or frequency accuracy. Here we demonstrate OODR spectroscopy using a cavity-enhanced frequency comb probe that combines all these advantages. We detect and assign sub-Doppler transitions in the spectral range of the 3$\nu$${}_3$$\leftarrow$$\nu$${}_3$ resonance of methane with frequency precision and sensitivity more than an order of magnitude better than before. This technique will provide high-accuracy data about excited states of a wide range of molecules that is urgently needed for theoretical modeling of high-temperature data and cannot be obtained using other methods.

Addendum added on Aug 20, 2024, containing comparison of experimental line positions and intensities to new predictions from an effective Hamiltonian and the ExoMol database

References in corpus (5)

• A hybrid line list for CH${}_4$ and hot methane continuum
• Formation of the Methyl Cation by Photochemistry in a Protoplanetary Disk
• Investigating the detectability of hydrocarbons in exoplanet atmospheres with JWST
• Sub-Doppler optical-optical double-resonance spectroscopy using a cavity-enhanced frequency comb probe
• Polarization-dependent Intensity Ratios in Double Resonance Spectroscopy

Cited by in corpus (9)

• 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
• Combined frequency comb and continuous wave cavity-enhanced optical-optical double-resonance spectrometer in the 1.7 $\mu$m range
• Assignment of collision-induced four-level double-resonance transitions in the 3$\nu$${}_3$ $\Leftarrow$ $\nu$${}_3$ spectral region of methane
• 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
• Rovibrational energy levels of H${}_2$O by quantum computing
• Theory of Lineshapes in Optical-Optical Double Resonance Spectroscopy
• Optical frequency comb double-resonance spectroscopy of the 9030-9175 cm${}^{-1}$ states of ethylene