Massively parallel sensing of trace molecules and their isotopologues with broadband mid-IR frequency combs produced via optical subharmonic generation

Abstract

We present a new platform for mid-infrared (MIR) dual-comb spectroscopy, based on a pair of ultra-broadband subharmonic optical parametric oscillators (OPOs) pumped by two phase-locked thulium-fiber combs. Our system provides fast (7 ms for a single interferogram), moving-parts-free, simultaneous acquisition of 350,000 spectral data points, spaced by 115-MHz intermodal interval over 3.1–5.5 μm spectral range. Parallel detection of 22 trace molecular species in a gas mixture, including isotopologues containing such isotopes as 13C, 18O, 17O, 15N, 34S, 33S and 2H (deuterium), with part-per-billion sensitivity and sub-Doppler resolution has been demonstrated. We also show that by utilizing Kerr-lens mode-locked Cr:ZnS lasers operating at λ≈2.35 μm one can create MIR frequency combs spanning almost two octaves in wavelength.