Comb-locked cavity ring-down saturation spectroscopy.

Area of Science:

• Atomic, Molecular and Optical Physics
• Spectroscopy
• Quantum Optics

Background:

• Precise measurement of molecular ro-vibrational transitions is crucial for various scientific fields.
• Traditional Lamb-dip spectroscopy faces limitations in accuracy and sensitivity for weak molecular lines.

Purpose of the Study:

• To introduce a novel comb-locked cavity ring-down spectroscopy method.
• To achieve high-accuracy Lamb-dip measurements of molecular ro-vibrational transitions.
• To demonstrate the technique's capability for weak transition lines.

Main Methods:

• Locking a probe laser frequency to an optical frequency comb.
• Stabilizing a high-finesse optical cavity to the same frequency comb.
• Utilizing comb-locked cavity ring-down spectroscopy for saturation spectroscopy.
• Measuring the R(9) line in the υ = 3 - 0 overtone band of CO.

Main Results:

• Achieved kilohertz accuracy in saturation spectroscopy of molecules.
• Successfully recorded the Lamb-dip spectrum of a weak CO overtone line (transition rate 0.0075 s⁻¹).
• Determined the transition line position with an uncertainty of 7 kHz (δν/ν∼3.5×10⁻¹¹).
• Demonstrated the technique's effectiveness with low input laser power (3 mW).

Conclusions:

• The comb-locked cavity ring-down spectroscopy method offers unprecedented accuracy for molecular spectroscopy.
• This technique is particularly valuable for studying weak ro-vibrational transitions.
• The current accuracy is limited by the external rubidium clock, suggesting potential for further improvement.