Mid-infrared Fourier transform spectroscopy with a broadband frequency comb

TLDR

Optical frequency‑comb‑based high‑resolution spectrometers promise powerful spectroscopic applications, yet the absence of suitable mid‑infrared comb sources has limited molecular fingerprinting. Here we present for the first time a frequency‑comb Fourier transform spectrometer operating from 2100 to 3700 cm⁻¹ that enables fast, simultaneous broadband absorption measurements with 0.0056 cm⁻¹ resolution. The system employs a broadband frequency comb in a Fourier transform spectrometer covering 2100‑3700 cm⁻¹, achieving 0.0056‑cm⁻¹ resolution and rapid, simultaneous broadband absorption acquisition. The instrument attains part‑per‑billion detection limits in 30‑second integrations for methane, ethane, isoprene, and nitrous oxide, accurately measures concentrations in complex gas mixtures, detects sub‑noise‑floor molecules through simultaneous spectral analysis, and offers near real‑time, high‑resolution, high‑bandwidth performance suitable to replace conventional FT spectrometers in trace‑gas, atmospheric, and medical diagnostics.

Abstract

Optical frequency-comb-based-high-resolution spectrometers offer enormous potential for spectroscopic applications. Although various implementations have been demonstrated, the lack of suitable mid-infrared comb sources has impeded explorations of molecular fingerprinting. Here we present for the first time a frequency-comb Fourier transform spectrometer operating in the 2100-to-3700-cm-1 spectral region that allows fast and simultaneous acquisitions of broadband absorption spectra with up to 0.0056 cm-1 resolution. We demonstrate part-per-billion detection limits in 30 seconds of integration time for various important molecules including methane, ethane, isoprene, and nitrous oxide. Our system enables precise concentration measurements even in gas mixtures that exhibit continuous absorption bands, and it allows detection of molecules at levels below the noise floor via simultaneous analysis of multiple spectral features. This system represents a near real-time, high-resolution, high-bandwidth mid-infrared spectrometer which is ready to replace traditional Fourier transform spectrometers for many applications in trace gas detection, atmospheric science, and medical diagnostics.