Mid-infrared supercontinuum-based Fourier transform spectroscopy for plasma analysis

Broadband mid-infrared (MIR) spectroscopy is a well-established and valuable diagnostic technique for reactive plasmas. Plasmas are complex systems and consist of numerous (reactive) types of molecules; it is challenging to measure and control reaction specificity with a good sensitivity. Here, we demonstrate the first use of a novel MIR supercontinuum (SC) source for quantitative plasma spectroscopy. The SC source has a wide spectral coverage of 1300-2700 cm−1 (wavelength range 3.7-7.7 μm), thus enabling broadband multispecies detection. The high spatial coherence of the MIR SC source provides long interaction path lengths, thereby increasing the sensitivity for molecular species. The combination of such a SC source with a custom-built FTIR spectrometer (0.1 cm−1 spectral resolution) allows detection of various gases with high spectral resolution. We demonstrate its potential in plasma applications by accurate identification and quantification of a variety of reaction products (e.g. nitrogen oxides and carbon oxides) under low-pressure conditions, including the molecular species with overlapping absorbance features (e.g. acetone, acetaldehyde, formaldehyde, etc.).