By using a compact duo of few-cycle Cr:ZnS lasers as a pump source and using optical rectification in ZGP crystal, we demonstrate high-resolution dual-comb spectroscopy in the long-wave infrared (LWIR) region. By recording a sequence of 1500 interferograms, we resolved the comb modes with the finesse exceeding 1000; LWIR spectra of several molecules including methanol, nitrous oxide, and ammonia were recorded in real time (1-10 sec) with 80-MHz (comb spacing) resolution with ~300,000 spectral points (comb modes), and the signal-to-noise ratio of ~100.
We present our recent results on the producing of ultra-broadband frequency combs in the mid-IR – THz range and their applications in dual-comb spectroscopy (DCS) that feature: sub-Doppler resolution, sensitivity down to part-per-billion level, and up to video-rate acquisition speed. We describe two techniques for generating frequency combs: (i) subharmonic generation in a sync-pumped optical parametric oscillator (OPO), which converts the carrier of ultrafast pulses to half that frequency and augments the spectrum to more than one octave, and (ii) optical rectification from few-optical-cycle 2.4- μm mode-locked lasers that produces a frequency downconverted output in the whole range from 1.5 to 50 THz and with the frequency span up to two octaves (e.g. 7.5–30 μm). We describe two approaches to the spectroscopic technique: (i) DCS with two mutually coherent mid-IR beams, and (ii) DCS with electro-optic sampling (EOS).
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