Double-resonance spectroscopy of methane using an optical frequency comb probe

Satellite- and ground-based observations of hot-Jupiter exoplanets revealed the presence of methane in their atmospheres. The observed spectra carry information about the thermodynamic conditions and chemistry at those exoplanets. To extract it, we need accurate theoretical models of the spectra verified by high-precision laboratory measurements.

However, the structure of the highly excited levels of methane is not fully understood, which precludes accurate modeling of the observed high-temperature spectra.

We will use sub-Doppler double-resonance spectroscopy with a mid-infrared continuous wave pump and a near-infrared frequency comb probe to measure hundreds of yet unexplored transitions to highly excited levels of methane with unprecedented combination of bandwidth, resolution and sensitivity.

The comb spectra will be recorded using a Fourier transform spectrometer, and high absorption sensitivity will be obtained by the use of enhancement cavity for the comb probe.

The transitions will be assigned using the line intensity ratios measured with parallel and perpendicular pump/probe polarizations.

Our project will provide data needed to verify theoretical calculations used to model the high-temperature spectra of hot-Jupiter exoplanets.

This data, which cannot be obtained by other means, is particularly important in the age of the planned NASA and ESA missions aimed at infrared spectroscopy of exoplanets.