The dielectric constant of the normal corneal tissue of a rabbit eye was obtained in vitro in the range from approximately 0.1 to 1 THz, and the drying process on the eye surface exposed to high-power terahertz waves was investigated by in vivo reflectance measurement using terahertz time-domain spectroscopy. When the rabbit eye was exposed to terahertz waves at 162 GHz for 6 min with an irradiation power of 360 or 480 mW/cm², the reflectance temporally increased and then decreased with a temperature increase. Based on multiple-reflection calculation using the dielectric constant and anterior segment optical coherence tomography images, those changes in reflectance were attributed to drying of the tear and epithelium of the cornea, respectively. Furthermore, the drying progressed over a temperature increase of around 5°C under our exposure conditions. These findings suggest that the possibility of eye damage increases with the progress of drying and that the setting of the eye surface conditions can be a cause of disagreement between computational and experimental data of absorbed energy under high-level irradiation because reflectance is related to terahertz wave penetration in the eye tissue. The time-domain spectroscopic measurements were useful for the acquisition of the dielectric constant as well as for the real-time monitoring of the eye conditions during exposure measurement.

The terahertz and infrared frequency vibration modes of room-temperature ionic liquids with imidazolium cations and halogen anions were extensively investigated. There is an intermolecular vibrational mode between the imidazolium ring of an imidazolium cation, a halogen atomic anion with a large absorption coefficient and a broad bandwidth in the low THz frequency region (13–130 cm⁻¹), the intramolecular vibrational modes of the alkyl-chain part of an imidazolium cation with a relatively small absorption coefficient in the mid THz frequency region (130–500 cm⁻¹), the intramolecular skeletal vibrational modes of an imidazolium ring affected by the interaction between the imidazolium ring, and a halogen anion with a relatively large absorption coefficient in a high THz frequency region (500–670 cm⁻¹). Interesting spectroscopic features on the interaction between imidazolium cations and halogen anions was also obtained from spectroscopic studies at IR frequencies (550–3300 cm⁻¹). As far as the frequency of the intermolecular vibrational mode is concerned, we found the significance of the reduced mass in determining the intermolecular vibration frequency.

The absorption characteristics of the dermis were reviewed in the terahertz range from 0.2 to 2 THz. The absorption magnitude of the dermis was higher than that of the epidermis model owing to the inclusion of collagen fibers. The heat denaturation of the collagen and the decrease of water content in the dermis caused a decrease in the absorption magnitude of the dermis. We verified that the absorption magnitude of collagen sheets at 1 THz similarly decreased by nearly 43% upon the heat treatment at approximately 70° C. When the heat-treated sheet was used as a scaffold for cell culture, the average growth rate of the fibroblast increased. These findings suggest that variation in the ability of cell growth in the dermis can be predicted using the absorption of the collagen or the difference between the absorptions of dermis and water.

In this study, an on-board calibration hot load (CHL) unit was developed for a terahertz sensing system (THzSens) receiver at 480 GHz to observe the emission lines of water and oxygen in the atmosphere. The compact CHL unit can be mounted on a microsatellite. We propose an accurate calibration method and a unit compact in design. We conducted experiments in order to obtain the best possible return loss value below the required −60 dB for calibration. The CHL unit uses two specular reflection absorber (SRA) plates and a radar absorbing material (RAM) as the absorber termination. The absorbers are assembled in a lightweight case made of carbon-fiber-reinforced plastics. The SRAs are placed at the Brewster angle with respect to the incident radiation to minimize reflection, which was found experimentally at 480 GHz. The CHL design is expected to have less than −78 dB reflection loss including SRA back scattering at 480 GHz. The return loss as a function of frequency for this design is below −60 dB, meeting the design requirements. Further, a compact prototype CHL was manufactured based on the proposed quasi-optical design. The new CHL for 480 GHz is 1/10 in the volume of the previous SMILES CHL for 650 GHz. The manufactured CHL prototype will be evaluated as a calibrator using the transmitter/receiver setup used in this study.