We measured the binding-state-dependent power absorptions, refractive indices, and dielectric constants of triple-stranded helices (TSHs) and single-stranded helices (SSHs) $\beta$ -glucans in laminarin using terahertz time-domain spectroscopy (TDS). The SSH $\beta$ -glucan was obtained from a TSH $\beta$ -glucan laminarin by a chemical treatment with NaOH solution. The power absorption of TSH $\beta$ -glucan increased more rapidly than that of the SSH $\beta$ -glucan with the frequency increment. The refractive index and dielectric constants of TSH $\beta$ -glucan were also larger than those of the SSH $\beta$ -glucan. This result implies that terahertz-TDS is a very effective method in classifying the conformational state of $\beta$ -glucans.

The utility of terahertz time-domain spectroscopy (THz-TDS) for the qualitative and quantitative analysis of edible oils remains underexplored. Therefore, we aimed to characterize an edible oil mixture consisting of perilla, soybean, and corn oils using THz-TDS spectroscopy and compare the findings with those from Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H NMR) spectroscopy. THz-TDS was used to obtain complex optical constants such as power absorption and refractive index of oils in the range of 0.2-2.0 THz. Perilla oil mixtures were quantitatively analyzed using complex dielectric constants in the THz frequency region. We characterized the double bond structure of omega-3 in perilla oil using THz-TDS. Furthermore, we used reflection-mode THz-TDS imaging to demonstrate its application as a non-destructive authenticity test for bottled edible oil.

We experimentally modulate the refractive index and the absorption coefficient of an SU-8 dry film in the terahertz region by UV light (362 nm) exposure with time dependency. Consequently, the refractive index of SU-8 film is increased by approximately 6% after UV light exposure. Moreover, the absorption coefficient also changes significantly. Using the reflective terahertz imaging technique, in addition, we can read security information printed by UV treatment on an SU-8 film that is transparent in the visible spectrum. From these results, we successfully demonstrate security printing and reading by using photoresist materials and the terahertz technique. This investigation would provide a new insight into anti-counterfeiting applications in fields that need security.