Abstract
Mid-infrared dual-comb spectroscopy offers interesting applications since molecules have their strongest rotational–vibrational absorptions in this frequency domain. Besides, generating frequency combs with electro-optic modulators recently showed promising results toward dual-comb spectroscopy. Here, we report a conversion in the mid-infrared of two mutually coherent frequency combs generated with electro-optic modulators to perform dual-comb spectroscopy in this region. Using fourth-order modulation instability taking place in the normal dispersion regime of a highly nonlinear fiber and by seeding this phenomenon with a frequency agile and low-power laser around 1.3 μm, we develop a stable and wavelength tunable all-fibered dual-comb spectrometer operating in the 2 μm region. This allows us to investigate CO2 absorption spectra over 37 nm and to measure collisional broadening coefficients of a few rotational–vibrational lines.
Highlights
Mid-infrared dual-comb spectroscopy offers interesting applications since molecules have their strongest rotational–vibrational absorptions in this frequency domain
We experimentally demonstrated a straightforward novel technique to convert an electro-optic modulators (EOM)-based dual comb from the C/L bands to the 2 μm region by fourth-order modulation instability in the normal dispersion regime of a highly nonlinear optical fiber
With a single idler continuous wave laser of only a few tens of milliwatts and since the nonlinear optical fiber used for wavelength conversion is common to the two combs, we showed that two pump combs can be converted while preserving their mutual coherence with no active stabilization, which significantly reduces the experimental complexity compared to systems based on mode-locked femtosecond lasers
Summary
Mid-infrared dual-comb spectroscopy offers interesting applications since molecules have their strongest rotational–vibrational absorptions in this frequency domain. Using fourth-order modulation instability taking place in the normal dispersion regime of a highly nonlinear fiber and by seeding this phenomenon with a frequency agile and low-power laser around 1.3 μm, we develop a stable and wavelength tunable all-fibered dual-comb spectrometer operating in the 2 μm region This allows us to investigate CO2 absorption spectra over 37 nm and to measure collisional broadening coefficients of a few rotational–vibrational lines. Two pump combs with slightly different repetition frequencies counter-propagate into a normally dispersive highly nonlinear silica fiber with a low power idler CW laser frequency agile in the O telecommunication band (1.29–1.31 μm) This way, a 4MI frequency conversion is seeded and results with the generation of two signal combs around 2 μm. DCS performed on the CO2 molecule reveals a good sensitivity of our setup and an excellent agreement with the HITRAN molecular spectroscopic database
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