Spectroscopy of the methaneν3band with an accurate midinfrared coherent dual-comb spectrometer

Abstract

We demonstrate a high-accuracy dual-comb spectrometer centered at 3.4 μm. The amplitude and phase spectra of the P, Q, and partial R branches of the methane ν 3 band are measured at 25 to 100 MHz point spacing with resolution under 10 kHz and a signal-to-noise ratio of up to 3500. A fit of the absorbance and phase spectra yields 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 10-fold improvement over Fourier transform spectroscopy. These data quantify the accuracy and resolution achievable with direct comb spectroscopy in the midinfrared.

Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator

“…Advances in mid-infrared (MIR) frequency comb sources have made possible broadband high-resolution absorption spectroscopy in the molecular fingerprint region [1,2] allowing simultaneous multispecies detection [3] and precision line position measurements [4]. The coherence of comb sources enables measurements over long distances [5] and efficient coupling to multipass cells [3] and cavities [6] to enhance the interaction length with the sample.…”

“…Fourier transform spectroscopy (FTS) can be implemented either with a mechanical interferometer [3,[7][8][9][10][11] or using the dual-comb technique [4,12,13]. Both approaches enable measurements with frequency resolution and precision provided by the comb with no influence of the instrumental line shape and are suitable for broadband precision spectroscopy [4,14].…”

“…The relative frequency scale is calibrated using a Fabry-Perot etalon or, alternatively, the galvo scanner position signal. We measure spectra of a calibrated CH 4 gas sample as well as dry and laboratory air and extract CH 4 and H 2 O concentrations by multiline fitting of model spectra. The figure of merit of the spectrometer is 1.7 × 10 −9 cm −1 Hz −1/2 per spectral element and the minimum detectable concentration of CH 4 is 360 ppt Hz −1/2 , averaging down to 90 ppt after 16 s.…”

On-chip dual-comb based on quantum cascade laser frequency combs

“…Nonetheless, optical sources capable of generating MIR frequency combs are extremely complex 8,[12][13][14][15] and dualcomb spectroscopy on the MIR range is only possible in highly equipped laboratories 10,11 . Instead, a compact dual-comb spectrometer in the MIR range could bring broadband high-precision measurements to practical applications such as trace gas or breath analysis, just to name a few.…”

“…Extending this technique to the MIR range 8 , where the fundamental roto-vibrational transitions of most gas molecules are present, will allow to achieve dual-comb spectroscopy measurements with accuracies and precisions never achieved [9][10][11] .…”