In this work, we studied the photocatalytic degradation of methyl orange (MO) dye using gold nanoparticles (AuNPs) synthesized by pulsed laser ablation in liquids (PLAL). The size, morphology, and optical properties of the synthesized AuNPs were determined using transmission electron microscopy (TEM) and UV-Vis spectroscopy. TEM analysis confirmed the formation of AuNPs that are mainly spherical, with particle size increasing as the number of laser pulses increases (250, 500 and 750 pulses) due to coalescence. The photocatalytic activity of the AuNPs was studied by monitoring the degradation of the MO dye under infrared (IR) irradiation for 60 min. The degradation efficiency was recalculated by η=( A_0-A_t )/A₀×100, and it was observed that the efficiency increases with the irradiation time for all the tested samples. Degradation efficiencies of 64
A convex-mirror-based aerial imaging by retro-reflection (AIRR) system can extend the floating distance and enlarge aerial images while maintaining a compact optical configuration. However, this system suffers from reduced light utilization efficiency and specular reflection from the beam splitter because the image-forming light passes through the beam splitter multiple times. In this study, we propose two polarization-modulated optical configurations for convex-mirror-based AIRR. The first configuration employs a reflective polarizer and two λ/4 retarder films to improve the apparent brightness of enlarged aerial images. The second configuration employs a λ/4 retarder film and an additional linear polarizer placed in front of the observer to suppress specular reflection from the beam splitter. Experimental results show that the convex-mirror-based p-AIRR system maintained the floating-distance extension and image magnification of the conventional convex-mirror-based AIRR system, achieving a floating distance of 830 mm and an image magnification of 3.4× at a light-source-to-reflective-polarizer distance of 500 mm. In addition, the observation-side polarization-control configuration visually suppressed beam-splitter-originated specular reflection while preserving the aerial image. These results indicate that polarization modulation is useful for improving the visibility of enlarged aerial images in convex-mirror-based AIRR systems.
A form-birefringent polarization converter fabricated on a fused-silica substrate with subwavelength grating structures was used to generate a cross-polarized femtosecond laser beam. The converter produces a beam with a fourfold rotationally symmetric polarization distribution and a doughnut-shaped intensity profile. Two quarter-wave elements were stacked to realize an effective half-wave polarization converter for operation at a wavelength of 800 nm. The generated beam was focused onto a 0.1-mm-thick stainless-steel plate using a 1-kHz femtosecond Ti: sapphire laser. A square through-hole with a side length of approximately 35 μm was obtained at a pulse energy of 45 µJ using 4000 pulses. The hole was circular at the laser-irradiated surface, whereas it became square inside the material and at the exit surface. The difference in optical absorption between P- and S-polarized components at the inclined sidewalls is considered to be a major factor in the formation of the square hole. These results demonstrate that the form-birefringent polarization converter provides an effective optical tool for structured-beam generation and noncircular laser micromachining.
Terahertz (THz) waves have broad application prospects in various fields due to their low photon energy, high bandwidth, and high spectral resolution. However, the development of efficient and low-loss waveguide devices remains a core bottleneck in advancing THz technology. This study investigates the tungsten (W)-based metal wire as effective THz waveguides. Using a combination of analytical and simulation methods, we systematically examine the frequency- and geometry-dependent modal properties. The results indicate that the single-wire waveguide supports a TM mode, while the double-wire waveguide supports a quasi-TEM mode. Meter-scale propagation lengths are achieved (R > 400 μm for the single wire and d > 8 mm for the double-wire waveguide, where R is the radius and d is the spacing), exceeding previously reported values for W metal wire waveguides. The structural parameters significantly influence the modal properties: the propagation length decreases with increasing frequency f, while it increases with the single-wire radius R, double-wire spacing d, and the ratio of R2/R1. These findings provide theoretical support for the design of low-loss THz metal wire waveguides in high-performance THz functional systems.
Although there are various methods for displaying floating images, many methods are flat floating images using 2D light sources. When viewing these floating images, we often perceive a pseudo-three-dimensional sensation (referred to as pseudo-3D perception in this paper) despite them being flat. Previous studies have reported the factors that affect the pseudo-3D perception, but they have focused exclusively on virtual images, with no reports on real images. Furthermore, although blur occurs in real image formation using methods such as AIRR and DCRA, the effect of blur on pseudo-3D perception has not been evaluated. In this paper, we conducted evaluation experiments on these factors. We experimentally clarified that, even for real images, pseudo-3D perception is improved by a decrease in background luminance, a decrease in contrast, and the addition of motion to the floating image. Additionally, we experimentally clarified that pseudo-3D perception decreases when a flat floating image is blurred.
