Selection rules for the orbital angular momentum of optically produced THz radiation

Terahertz continuous wave spectroscopy: a portable advanced method for atmospheric gas sensing

Motivated by the increasing demand to monitor the air-quality, our study proved the feasibility of a new compact and portable experimental approach based on Terahertz (THz) continuous wave high resolution spectroscopy, to detect the presence of the air's contaminants as greenhouse gases (GHG) and volatile organic compounds (VOCs). In this specific work, we first characterized, determining their molar absorption coefficient in the spectral region (0.06-1.2) THz, the pure optical response of the vapor of five VOCs: methanol, ethanol, isopropanol, 1-butanol and 2-butanol. In particular, 1-butanol and 2-butanol are characterized for the first time in literature at THz frequencies. Then we studied the optical response of their mixtures achieved with ambient air and ethanol. The results show that it is possible for a differentiation of single components by describing their spectral absorption in terms of the linear combination of pure compounds absorption. This proof of concept for this apparatus study and set-up paves the way to the use of THz Continuous wave high resolution spectroscopy for the environmental tracking of air pollutants.

Terahertz Spectroscopic Analysis in Protein Dynamics: Current Status

Proteins play a key role in living organisms. The study of proteins and their dynamics provides information about their functionality, catalysis and potential alterations towards pathological diseases. Several techniques are used for studying protein dynamics, e.g., magnetic resonance, fluorescence imaging techniques, mid-infrared spectroscopy and biochemical assays. Spectroscopic analysis, based on the use of terahertz (THz) radiation with frequencies between 0.1 and 15 THz (3–500 cm−1), was underestimated by the biochemical community. In recent years, however, the potential of THz spectroscopy in the analysis of both simple structures, such as polypeptide molecules, and complex structures, such as protein complexes, has been demonstrated. The THz absorption spectrum provides some information on proteins: for small molecules the THz spectrum is dominated by individual modes related to the presence of hydrogen bonds. For peptides, the spectral information concerns their secondary structure, while for complex proteins such as globular proteins and viral glycoproteins, spectra also provide information on collective modes. In this short review, we discuss the results obtained by THz spectroscopy in the protein dynamics investigations. In particular, we will illustrate advantages and applications of THz spectroscopy, pointing out the complementary information it may provide.