We report on a prototypical study of the detection of microplastic embedded in table salts by using terahertz time-domain spectroscopy. In the experiment, high-density polyethylene (HDPE) of sizes from 150 to 400 μm are used as a representative microplastic and mixed with table salts. Analyzing terahertz transmittance with an effective medium model, we extract various optical properties such as refractive index, absorption coefficient, and real/imaginary parts of the dielectric constant of the mixture. Consequently, the optical properties exhibit volume-ratio-dependence in 0.1–0.5 THz regimes. Especially, the refractive index and the real part of the dielectric constant possess monotonic frequency dependence, meaning that the quantities can be relevant indicators for the detection of the microplastic in terms of practical applications. Our work proves that terahertz time-domain spectroscopy can pave a way to recognize microplastic mixed with salts and be expanded for detecting various micro-sized particles.

We demonstrate excitons and trions in bulk ReS2 at low temperatures using polarization-resolved photoluminescence (PL) spectroscopy. At 70 K, two excitons (near 1.543 and 1.576 eV) and trions (near 1.517 and 1.570 eV) with anisotropic polarization features are observed, similar with those of a thin layer. We attribute the emergence of excitons and trions in the bulk ReS2 to its weak interlayer coupling, which is distinct from typical 2D semiconductors. Based on the assignment, we further investigate incident-laser-power dependence, providing power exponents for the quasiparticles. We expect that our basic characterization of bulk ReS2 can contribute to understand various quasiparticles and their optical applications.

No abstract

No abstract