The ability to detect and measure a variety of gases under certain environmental conditions has significant
potential impact in many areas; from hazardous gas detection in the industrial domain to physical sciences
in academia. Gas sensing has long received attention with microwave and infrared spectroscopy. With many
molecular resonances occurring in the THz (T-ray) range leading to simple, unique spectral features, THz time-domain
spectroscopy (TDS) promises to be a potential tool for gas detection. This paper presents a preliminary
study on real-time gas recognition with THz-TDS. In particular, a simple method is proposed that involves
extracting line positions from gas species without a reference pulse and classifying them by means of the minimum
Euclidean distance using the Submillimeter, Millimeter, and Microwave Spectral Line Catalog.
Measurement precision is often required in the process of material parameter extraction. This fact is applicable
to terahertz time-domain spectroscopy (THz-TDS), which is able to determine the optical/dielectric constants of
material in the T-ray regime. Essentially, an ultrafast-pulsed THz-TDS system is composed of several mechanical,
optical, and electronic parts, each of which is limited in precision. In operation, the uncertainties of these
parts, along with the uncertainties introduced during the parameter extraction process, contribute to the overall
uncertainty appearing at the output, i.e. the uncertainty in the extracted optical constants. This paper analyzes
the sources of uncertainty and models error propagation through the process.
Terahertz (THz) imaging offers many attractive advantages over existing modalities especially in its ability
to obtain spectroscopic information. In particular, THz spectra are extremely sensitive to small changes of
the molecular structure and different isomeric and intermolecular configurations. With a comparatively longer
wavelength (0.3 mm at 1 THz), THz images suffer from the problem of low spatial resolution, as determined by
Rayleigh's criterion and proves to be a major limitation. This paper reviews the existing THz near-field methods
and recent developments for identifying potential areas of research.
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