We fabricated a terahertz wire-grid polarizer consisting of a micrometer-pitch Al grating on a Si substrate by photolithography and wet etching. The ratio of TM and TE transmittances (extinction ratio) was over $35\mathrm{dB}$ at $0.5\mathrm{THz}$. At the Brewster angle of the Si substrate, the polarization transmittance of a TM wave through the fabricated polarizer exceeded 95% and the extinction ratio was over $45\mathrm{dB}$ at $\sim 1\mathrm{THz}$. The fabricated polarizer has a higher extinction ratio than conventional free-standing terahertz wire-grid polarizers.

Microstructures in nature are ultrafine and ordered in biological roles, which have attracted material scientists. Spirulina forms three-dimensional helical microstructure, one of remarkable features in nature beyond our current processing technology such as lithography in terms of mass-productivity and structural multiplicity. Spirulina varies its diameter, helical pitch, and/or length against growing environment. This unique helix is suggestive of a tiny electromagnetic coil, if composed of electro-conductive metal, which brought us main concept of this work. Here, we describe the biotemplating process onto Spirulina surface to fabricate metal microcoils. Structural parameters of the microcoil can be controlled by the cultivation conditions of Spirulina template and also purely one-handed microcoil can be fabricated. A microcoil dispersion sheet exhibited optically active response attributed to structural resonance in terahertz-wave region.

[[abstract]]Super-fine ink-jet (SIJ) printing technology is applied to the fabrication of terahertz metamaterials. A silver film is fabricated using an SIJ printer with silver paste ink, and it is confirmed that the film behaves as a good conductor in the terahertz frequency region. Then, basic terahertz metamaterials such as metal wire-grid structures and split-ring resonators are printed on high-resistivity silicon substrates. The terahertz responses of the printed samples agree with those expected from their structures. SIJ printing is one of the ideal methods for fabricating terahertz metamaterials owing to its rapidity, simplicity, flexibility, and sufficient accuracy.[[fileno]]2010144010186[[department]]物理

Wire-grid polarizer sheets in the terahertz region have been fabricated on flexible substrates by nanoimprint technology. They show an ideal polarization property in the terahertz frequency region, whereas the cost is very low. Since the wire pitch is far smaller than the wavelength, the effective medium theory agrees well with experimental results. The effective medium theory shows the possibility of further improvement of polarization properties by selecting appropriate materials for wire grids.

Quasi-monodisperse dielectric particles organized in a periodic hexagonal network on an aluminum surface are exploited numerically and experimentally as a single-layered near-perfect absorber in the terahertz regime. Of particular interest are titanium dioxide (${\mathrm{TiO}}_2$) microspheres because of their large dielectric permittivity and isotropic shape leading to Mie resonances with insensitive polarization. Absorption higher than 80% at normal incidence covering two distinct ranges of frequencies is demonstrated experimentally. Furthermore, the performance of the metamaterial absorber is kept over a wide range of incident angles.

With rapid advances occurring in terahertz (THz) radiation generation techniques, the interaction between matter and intense THz fields has become an important research topic. Among different types of THz radiation sources, the free electron laser (FEL) is a promising experimental tool that is expected to pave the way for new forms of material processing, control of phase transitions, and serve as a test bench for extreme operating conditions in high-speed small-size electrical and magnetic devices through the exploitation of strong THz electrical and magnetic fields without the presence of interband electronic excitation. In the current work, we irradiated Ge₂Sb₂Te₅ phase change memory material with intense THz pulse trains from an FEL and observed THz-induced surface changes due to damage as a precursor to ablation and the formation of fine surface undulations whose spatial period is comparable to or slightly smaller than the wavelength of the excitation THz pulses in the material. The formation of undulations as well as the fact that no significant thermal effect was observed below the volume expansion threshold suggests that THz-induced effects mainly contributed to the observed changes. To the best of our knowledge, this is the first experimental observation of THz-induced undulations (so-called “LIPSS”), which are of potential importance for laser material processing.