Tunable dual-comb spectrometer for mid-infrared trace gas analysis from 3 to 4.7 µm

Area of Science:

• Spectroscopy
• Laser Technology
• Analytical Chemistry

Background:

• Dual-frequency comb spectroscopy offers high resolution for wide-spanning spectra.
• It is a powerful technique for sensitive multi-component gas analysis.

Purpose of the Study:

• To present a novel spectrometer based on two electro-optical combs.
• To enable measurements in the mid-infrared range (3-4.7 µm) for gas analysis.

Main Methods:

• Utilized two electro-optical combs with tunable repetition rates (250-500 MHz).
• Employed tunable difference frequency generation for mid-infrared conversion.
• Achieved high signal-to-noise ratios (>10^5 in 1 s) with 440 detected comb modes at 500 MHz.

Main Results:

• Demonstrated coherence preservation within a 3-second measurement time.
• Successfully measured concentrations of methane (5 ppm at 3.3 µm), nitrous oxide (100 ppm at 3.9 µm), and a CO/CO2 mixture (15 ppm CO, 5% CO2 at 4.5 µm).
• Achieved a noise-equivalent absorption coefficient of 6.4(3) x 10^-6 cm^-1 Hz^-1/2.

Conclusions:

• The developed spectrometer is effective for sensitive, high-resolution multi-component gas analysis in the mid-infrared.
• The technique shows promise for various applications requiring precise gas concentration measurements.