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

Area of Science:

• Molecular Spectroscopy
• Astrophysical Chemistry
• Combustion Science

Background:

• Accurate molecular hot-band transition parameters are essential for modeling high-temperature spectra in astrophysics and combustion.
• Laboratory spectra at high temperatures are often unresolved and difficult to assign, hindering accurate data acquisition.

Purpose of the Study:

• To demonstrate a novel optical-optical double-resonance (OODR) spectroscopy technique for measuring hot-band transitions.
• To overcome limitations of previous OODR methods, including resolution, spectral coverage, sensitivity, and frequency accuracy.

Main Methods:

• Utilized optical-optical double-resonance (OODR) spectroscopy.
• Employed a cavity-enhanced frequency comb probe for enhanced performance.
• Detected and assigned sub-Doppler transitions in methane's 3ν₃←ν₃ resonance.

Main Results:

• Achieved over an order of magnitude improvement in frequency precision and sensitivity compared to previous methods.
• Successfully detected and assigned individual hot-band transitions without heating the sample.
• Demonstrated a combined approach offering superior resolution, spectral coverage, and absorption sensitivity.

Conclusions:

• The developed OODR spectroscopy technique provides high-accuracy data on molecular excited states.
• This method is crucial for theoretical modeling of high-temperature data in various scientific fields.
• Offers a unique capability for obtaining otherwise inaccessible molecular spectral data.