Time-resolved mid-Infrared dual-comb absorption and dispersion spectroscopy of methane and ethane: towards plasma applications

Broadband time resolved absorption and dispersion spectroscopy using a conventional Fourier transform spectroscopy is often a challenging task due to very long measurement times. Here, we present time resolved mid-infrared dual-comb absorption and dispersion spectroscopy of methane and ethane under electrical discharge, covering a spectral bandwidth of 2850-3150 cm-1, with spectral resolution of 5 GHz and temporal resolution of 20 µs. This new approach enabled the direct measure of broadband complex refractive index of materials involved in plasma, which is an indication of plasma density.