Terahertz time-domain spectroscopy (THz-TDS) at room temperature and standard atmosphere pressure remains so far the backbone of THz photonics in numerous applications for civil and defense levels. Plasmonic microstructures and metasurfaces are particularly promising for improving THz spectroscopy techniques and developing biomedical and environmental sensors. Highly doped semiconductors are suitable for replacing the traditional plasmonic noble metals in the THz range. We present a perfect absorber structure based on semiconductor III-Sb epitaxial layers. The insulator layer is GaSb while the metal-like layers are Si doped InAsSb (∼ 5·10 19 cm -3 ). The doping is optically measured in the IR with polaritonic effects at the Brewster angle mode. Theoretically, the surface can be engineered in frequency selective absorption array areas of an extensive THz region from 1.0 to 6.0 THz. The technological process is based on a single resist layer used as hard mask in dry etching defined by electron beam lithography. A wide 1350 GHz cumulative bandwidth experimental absorption is measured in THz-TDS between 1.0 and 2.5 THz, only limited by the air-exposed reflectance configuration. These results pave the way to implement finely tuned selective surfaces based on semiconductors to enhance light-matter interaction in the THz region.

The terahertz absorption spectra of sodium magnesium chlorophyllin (Chl-Mg-Na) and sodium copper chlorophyllin (Cu-Chl), two major members of the chlorophyll derivative family, have been measured in the range 0.2−2.5 THz, at room temperature. The capability of terahertz spectroscopy for quantitative characterization of Chl-Mg-Na intermolecular vibrations was investigated and the sensitivity of transitions with degree of hydration by changes in the molecular environment was examined. For the Cu-Chl derivative, a broad feature was observed around 1.8 THz which currently hinders clear Cu-Chl identification and quantification.

We apply reverse engineering techniques (RET) to analyze the dehydration process of a sunflower leaf with terahertz time-domain spectroscopy. The multilayer structure of the leaf is extracted with accuracy during the entire process. Time variations of thickness and the complex index are emphasized for all leaf layers (2 cuticules, 2 epiderms, and 2 mesophylls). The global thickness of the sunflower leaf is reduced by up to 40% of its initial value.

We apply reverse engineering techniques in the time domain THz regime to recover the multilayer structure of a sunflower leaf. Results are successful and allow to analyze the time sunflower behavior under water stress

Terahertz time-domain spectroscopy has been used to investigate the vibrational spectra of polycrystalline sodium magnesium chlorophyllin - one of the natural derivatives of chlorophyll - over the temperature range 88 K–298 K. A number of well-resolved absorption peaks were observed in the frequency range 0.2–2.5 THz, which are interpreted as originating from mixed character of intramolecular and intermolecular vibration modes. As the temperature is increased, the observed absorption features resolve into broader peaks. The peak centered at 1.83 THz shifts towards higher frequencies, indicating that for this feature, significant intermolecular anharmonicity exist.