Frequency-comb-based absolute frequency measurements in the mid-infrared with a difference-frequency spectrometer.

Area of Science:

• Metrology
• Spectroscopy
• Quantum Optics

Background:

• Optical frequency combs (OFCs) are advanced tools for precise frequency measurements.
• Extending OFC metrology to the mid-infrared (mid-IR) region is crucial for molecular spectroscopy.
• Current mid-IR frequency standards have limitations in density and quality.

Purpose of the Study:

• To extend the metrological performance of optical frequency combs to the mid-IR.
• To establish new, high-quality molecular frequency standards in the IR.
• To demonstrate precise frequency measurements of CO2 transitions in the mid-IR.

Main Methods:

• Phase locking pump and signal lasers of a difference-frequency source to an optical frequency comb.
• Utilizing cavity-enhanced saturated-absorption spectroscopy for high-resolution measurements.
• Measuring absolute frequencies of CO2 transitions near 4.2 micrometers.

Main Results:

• Successfully extended optical frequency comb metrology to the mid-IR region.
• Achieved an absolute frequency uncertainty of 800 Hz (1.1 x 10^-11) for CO2 transitions.
• Demonstrated the capability for precise spectroscopic measurements in the mid-IR.

Conclusions:

• The study confirms the feasibility of using OFCs for high-precision mid-IR spectroscopy.
• This work paves the way for a new generation of dense, high-quality molecular frequency standards in the IR.
• The demonstrated technique significantly enhances metrological capabilities in the mid-IR spectrum.