Fast molecular fingerprinting with a coherent, rapidly tunable dual-comb spectrometer near 3 μm.

Abstract

Molecular spectroscopy in the mid-infrared spectral range is expected to present fingerprints of chemical species that provide a unique identification with adequate sensitivity. Dual-comb spectroscopy, a promising successor to conventional Fourier-transform spectroscopy, enables rapid molecular fingerprinting with high-resolution and high-precision. Here, we report gas-phase transmittance and dispersion spectra by employing a rapidly tunable dual-comb spectrometer based on electro-optic frequency combs near 3 μm. The tunable spectral range >550 cm-1 and adjustable optical resolutions from a few hundred MHz to a few GHz were demonstrated. With the capabilities of wavelength agility and easily adjustable comb-mode spacing, the spectra of nitrous oxide and its isotopes were measured with Doppler-limited resolution. Furthermore, the N2-broadened spectra of acetylene were recorded to derive the collisional broadening coefficient. Fast acquisitions with adequate spectral resolution were also achieved within sub-microseconds. Both precision spectral metrology and fast molecular sampling could be implemented by employing the high-flexible dual-comb spectrometer.