Spectroscopy of the Methane {\nu}3 Band with an Accurate Mid-Infrared Coherent Dual- Comb Spectrometer

TL;DR

This paper presents a high-precision dual-comb spectrometer that measures methane's { u}3 band with unprecedented accuracy, enabling detailed rovibrational spectra analysis and significantly improving spectral measurement precision over traditional methods.

Contribution

The study introduces the first high-accuracy molecular spectra obtained with a direct comb spectrometer, achieving tenfold better precision than Fourier transform spectroscopy.

Findings

Measured 132 rovibrational lines with ~kHz resolution.

Achieved a systematic uncertainty of 300 kHz, 10^-3 of Doppler width.

Demonstrated high SNR up to 3500 in mid-infrared spectroscopy.

Abstract

We demonstrate a high-accuracy dual-comb spectrometer centered at 3.4 \mu m. The amplitude and phase spectra of the P, Q, and partial R-branch of the methane {\nu}3 band are measured at 25 MHz to 100 MHz point spacing with ~kHz resolution and a signal-to-noise ratio of up to 3500. A fit of the absorbance and phase spectra yield the center frequency of 132 rovibrational lines. The systematic uncertainty is estimated to be 300 kHz, which is 10-3 of the Doppler width and a tenfold improvement over Fourier transform spectroscopy. These data are the first high- accuracy molecular spectra obtained with a direct comb spectrometer.