NANOPHOTONIC SUPERCONTINUUM-BASED MID-INFRARED DUAL-COMB SPECTROSCOPY

Abstract

An optically stabilized dual-comb system is used to drive a mid-infrared spectroscopy for parallel gas-phase detection in the functional group region from 2800-3600 cm$^{-1}$. The system comprises two amplified ultra-low noise fiber frequency combs (\textbf{FC-1500-ULN from Menlo Systems}), centered at 1550 nm wavelength, which are spectrally broadened to the mid-IR by two chip-based $\text{Si}_3 \text{N}_4$ waveguides. The probe comb passes through a gas-cell containing CH$_4$ (430 ppm), C$_2$H$_2$ (420~ppm), and N$_2$ as a buffer gas and is eventually superimposed with the reference comb on a photodetector. The dual-comb spectrum below reveals the corresponding absorption features, with sufficient resolution to even resolve isotopologues. The present absorption feature of H$_2$O is due to interaction with water vapour during free-space propagation.

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