Accurate frequency referencing for fieldable dual-comb spectroscopy.

Area of Science:

• Spectroscopy
• Optical Physics
• Analytical Chemistry

Background:

• Traditional dual-comb spectrometers rely on external radio frequency (rf) and optical frequency references, limiting their field applicability.
• Achieving ultra-high spectral resolution and frequency accuracy typically requires complex laboratory setups.

Purpose of the Study:

• To develop and characterize a self-referencing dual-comb spectrometer for high-performance spectral measurements.
• To demonstrate the instrument's capability for accurate gas analysis in a field-deployable configuration.

Main Methods:

• A 'bootstrapped' frequency referencing scheme using free-running diode lasers for short-term coherence and a quartz oscillator for long-term accuracy.
• Characterization of sensitivity, stability, and accuracy using a multipass cell.
• Acquisition of high-resolution spectra of water and carbon dioxide transitions in the near-infrared region.

Main Results:

• Demonstrated comb-resolved spectra from 140 THz to 184 THz (2.14 µm to 1.63 µm) with 200 MHz frequency sampling and ~1 MHz accuracy.
• Molecular transmission measurements showed minimal deviation (< 5.6 × 10^-4) compared to maser/laser-referenced systems.
• Achieved a carbon dioxide detection sensitivity of 0.10 ppm-km with a 13-minute integration time at 1.60 µm.

Conclusions:

• The developed dual-comb spectrometer provides laboratory-grade spectral resolution and accuracy in a portable, self-referencing instrument.
• The system is suitable for field deployment, enabling accurate and sensitive molecular detection and quantification.
• This technology advances the potential for remote and in-situ spectroscopic analysis.