A laser-fabricated metallic resonator based on a double-slit array (DSA) is numerically and experimentally demonstrated at terahertz frequencies. Such free-standing resonators achieve a sharp resonance with high quality (Q) factor, arising from a distortion of symmetry-protected bound states in the continuum (BIC). By breaking the structural symmetry of DSAs, the BIC with infinite Q-factor can be transformed into quasi-BICs, and the Q-factors decrease gradually as the asymmetry parameter increases. We analyzed the influence of the imperfection in experimental samples such as the round edge and the trapezoid shape on the transmission properties of DSAs. Different from the DSAs composed of ideal perfect electrical conductors, copper DSAs show lower Q-factor because of the Ohmic loss. The effect of metal thickness on the quasi-BICs for DSAs is also investigated. Results exhibit that thinner resonators can achieve sharper quasi-BICs. These findings suggest that such metallic resonators with high Q-factors have great potential for practical applications in electromagnetic wave filtering and biomolecular sensing.

In this research, terahertz (THz) antireflective structures tapered with several profiles (linear, exponential, Klopfenstein) were modeled for high-resistivity silicon and theoretically evaluated using a high-frequency electromagnetic field simulation (HFSS). Their antireflective characteristics are greatly affected by the profiles. One-dimensional periodic tapered THz antireflective structures with different profiles were also fabricated on high-resistivity silicon using femtosecond laser processing. Their antireflective characteristics were experimentally evaluated by standard THz time-domain spectroscopy and modeled by HFSS for reference. The experimental results are in good agreement with the simulations, which showed that the Fresnel reflection reduces to almost zero over a band broader than 1 THz.

Molybdenum carbides (MoC and Mo₂C) are being reported for various applications, for example, catalysts for sustainable energies, nonlinear materials for laser applications, protective coatings for improving tribological performance, and so on. A one-step method for simultaneously fabricating molybdenum monocarbide (MoC) nanoparticles (NPs) and MoC surfaces with a laser-induced periodic surface structure (LIPSS) was developed by using pulsed laser ablation of a molybdenum (Mo) substrate in hexane. Spherical NPs with an average diameter of 61 nm were observed by scanning electron microscopy. The X-ray diffraction pattern and electron diffraction (ED) pattern results indicate that a face-centered cubic MoC was successfully synthesized for the NPs and on the laser-irradiated area. Notably, the ED pattern suggests that the observed NPs are nanosized single crystals, and a carbon shell was observed on the surface of MoC NPs. The X-ray diffraction pattern of both MoC NPs and LIPSS surface indicates the formation of FCC MoC, agreeing with the results of ED. The results of X-ray photoelectron spectroscopy also showed the bonding energy attributed to Mo-C, and the sp²-sp³ transition was confirmed on the LIPSS surface. The results of Raman spectroscopy have also supported the formation of MoC and amorphous carbon structures. This simple synthesis method for MoC may provide new possibilities for preparing Mo _x C-based devices and nanomaterials, which may contribute to the development of catalytic, photonic, and tribological fields.

A hybrid antireflective structure (ARS) is proposed for enhancing the transmittance of terahertz (THz) waves. This hybrid ARS was made by attaching a polymer-based two-layer coating onto a moth-eye structure on a silicon (Si) substrate. The measured power reflectance of this hybrid ARS remained below 6% in the frequency range of 0.6–2.5 THz, corresponding to the simulated results. The total power reflectance from 0.1 to 2.5 THz was 20% that of the unprocessed Si surface. Besides exhibiting a broadband AR characteristic, this hybrid ARS inherited the cleanable flat surface from the coating structure, which also acts as a protective shield for the moth-eye structures. This high-transmittance, cleanable, flat antireflective surface can not only improve the performance of numerous THz components but also promote the applications of THz waves in daily life.

A photoconductive detector (PCD) responding only to vacuum ultraviolet (VUV) radiations below 180 nm without any filter was fabricated using an yttrium fluoride (YF ₃ ) thin film grown by femtosecond (fs) laser pulsed laser deposition (PLD). The structural morphology (particle size and surface roughness) of the thin film was improved using a low laser fluence and a high substrate temperature during the fabrication. The smallest average particle size achieved was 159 nm with a roughness of 37 nm at a laser fluence of 13.5 J cm ⁻² and a substrate temperature of 400 °C. The resistances for the dark current of the PCD increased from 10 TΩ to 680 TΩ using YF ₃ thin films with a smaller average nanoparticle diameter of 159 nm rather than 330 nm. The time response of the PCD to a VUV flash lamp emitting at 170 nm showed that a small average nanoparticle diameter results to a fast response time. By covering the Al electrode pairs with another fs PLD-grown YF ₃ film, the influence of external photoelectric effect was suppressed and the response wavelength edge decreased from 280 nm to 180 nm without any filter. The filterless PCD is expected to enhance the use of fluoride thin films in conjunction with VUV light sources for various scientific and industrial applications.