Broadband Super-Resolution Terahertz Time-Domain Spectroscopy Applied to Gas Analysis

Commercially available terahertz (THz) time-domain spectroscopy (THz-TDS) apparatus is used in multiple application fields from material science to biology and even in the industry to measure the thickness of paint layers. Its broad spectral coverage is of interest for air quality monitoring and atmospheric composition analysis.However, gas spectroscopy needs high resolution that the usual approach in THz-TDS is unable to provide. In this article, we introduce the concept of constraint reconstruction for super-resolution spectroscopy based on the modeling of the spectroscopic rotational lines in a sparse spectrum.It is demonstrated for low-molecular weight molecules in the gas phase that typically have spectra containing a small number of narrow lines over a broad spectrum. This alternative approach directly reconstructing the spectra achieved a resolution improvement factor of 10 compared with the best available resolution by the standard THz-TDS data treatment.