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The goal of this study was to investigate a study for the efficient generation of pillar-like nanostructure (nanopillar) on a material surface over a large area. In this research, a vertical cross-scanning (VCS) strategy using two linearly-polarized lasers with different laser conditions was proposed for the generation of nanopillars on a mirror-polished surface on a large scale. It found that the laser fluence and scanning speed of the second laser scanning should be controlled within a specific range to generate the nanopillars. Additionally, the distance between scan lines, which is defined as hatch distance, h, of the second scan, is also a non-negligible factor to induce nanopillars to cover the entire surface. This work demonstrated that the VCS method is a feasible strategy for the fabrication of nanopillars on the entire mirror-polished surface of Ti6Al4V alloy by linearly-polarized picosecond laser conveniently and efficiently.

Compared with traditional nanotexturing methods, an ultrashort-pulsed laser is an efficient technology of fabricating nanostructures called laser-induced periodic surface structures (LIPSS) on material surfaces. LIPSS are easily fabricated when the pulse duration is shorter than collisional relaxation time (CRT). Accordingly, ultrashort-pulsed lasers have been mainly used to study LIPSS, but they unstably irradiate while requiring high costs. Although long-pulsed lasers have low cost and high stability, the phenomena (such as the effect of pulse duration, laser wavelength, and heat) of the LIPSS fabricated using short-pulsed lasers with the pulse duration close to the maximum CRT, which is greater than femtosecond, have not been clarified. However, the nanosecond pulse laser has been reported to produce LIPSS, but those were unclear and ununiform. In this study, the short-pulsed laser with the pulse duration of 20 ps, which is close to the maximum CRT, was employed to clarify the effects of pulse duration and heat on the fabrication of LIPSS and to solve problems associated with ultrashort-pulsed lasers. First, a finite-difference time-domain simulation was developed at 20-ps pulse duration to investigate the effects of irradiation conditions on the electric-field-intensity distribution. Subsequently, experiments were conducted using the 20-ps pulse laser by varying conditions. The aspect ratio of the LIPSS obtained was greater than that of the LIPSS fabricated using ultrashort-pulsed lasers, but LIPSS were not fabricated at 355- and 266-nm laser wavelength. In addition, the short-pulsed laser experienced thermal influences and a cooling material was effective for the fabrication of LIPSS with high-aspect-ratio. This demonstrates the effects of pulse duration close to the CRT and heat on the fabrication of LIPSS.

Electrochemical machining (ECM) is a well-established elution method with high processing speed, application to hard-to-cut material and less tool wear as noncontact between a workpiece and a tool. However, ECM is hard to process precisely and fabricate nanostructures. A short-pulsed laser (SPL), on the other hand, can fabricate fine periodic structures called as LIPSS (laser-induced periodic surface structures), which has been reported to provide materials with functionalities such as the reduction of friction, the change of wettability and the improvement of biocompatibility. Nevertheless, an SPL capable of fabricating nanostructures is unstable for the creation of large scale shapes. The appropriate processing method depends on the scale of the demanded shape and structure, and it takes long processing time with the complicated process to create the shape and fabricate nanostructures on the surface. The hybrid manufacturing process with an SPL and ECM (SPLECM) was then proposed to fabricate multiscale structures effectively, that an SPL increasing electric filed intensity enables ECM to improve the processing speed and fabrication of nanostructures on the electrochemical machined surface. In this study, the effects of the hybrid process with an SPL and ECM on the fabrication of multiscale structures on 304 stainless steel substrates were investigated experimentally. The proposed method capable of improving processing speed and fabricating multi-scale structures were stated. This study demonstrated the efficacy of SPLECM to create a shape and fabricate nanostructures on the surface simultaneously.

In this study, we propose a method to estimate oxygen saturation by selecting the best bands from video images captured by a multiband camera. Oxygen saturation is one of the most important bioindicators for measuring human health. For example, when a person contracts COVID-19, which is currently prevalent, oxygen uptake does not work properly and oxygen saturation drops without the person being aware of it, which may lead to severe symptoms. Monitoring oxygen saturation is very important so that the person receives treatment before such a situation occurs. The commonly used contact sensor is uncomfortable because of its pressure and it is difficult to wear on a daily basis, so non-contact estimation of oxygen saturation is desirable. To estimate oxygen saturation using a contact sensor, the difference in the absorption coefficients of oxidized hemoglobin and deoxidized hemoglobin is used. Using the same principle, it is possible to estimate oxygen saturation without contact using the signals from two channels obtained by an RGB camera. Currently, many smartphones are equipped with infrared cameras for face recognition, and increasingly more models are equipped with multi-camera systems consisting of RGB and infrared cameras. In such cases, it is difficult to take advantage of the multiple bands because the optimal combination of bands for oxygen saturation estimation varies depending on the imaging environment and the subject. In this study, to select the optimal combination of bands from multi-band video images, we used a Monte Carlo simulation of light scattering on the skin to simulate pulse waves during oxygen saturation changes while measuring the signals with a multi-band camera. We further propose a method to select the most accurate combination for estimating the oxygen saturation based on the features obtained from the pulse wave.

An active area of research is the altering of surface functions (e.g., wettability and cell adhesion) by controlling fine surface structures such as laser-induced periodic surface structures (LIPSS). It has been found that micrometer-scale grooving (produced, for example, using ultraprecision cutting) followed by short-pulsed laser irradiation can result in efficient LIPSS coverage of a large area. However, micrometer-scale grooves can remain on the surface after short-pulsed laser irradiation. In this paper, to clarify the phenomenon and processing principle of groove-assisted short-pulsed laser irradiation, a finite-difference time-domain simulation is developed and experiments are conducted using 304 stainless steel and nickel-phosphorus (Ni–P) plating layer substrates. The use of magnetic abrasive finishing (MAF) is proposed for fabricating sub-micrometer-deep straight grooves with various peak-to-peak distances (pitch length) prior to the short-pulsed-laser irradiation. The subsequent short-pulsed-laser irradiation produces sub-micrometer-deep straight structures superimposed on the MAF-produced surface. While the pattern and depth of LIPSS are influenced by the groove depth made by MAF prior to the short-pulsed laser irradiation, the pitch length of LIPSS is dependent on the laser wavelength. This demonstrates the ability of MAF to produce grooves that guide the LIPSS and the efficacy of the developed method for fabricating fine LIPSS. The geometry of the sub-micrometer deep grooves—made prior to the short-pulsed laser irradiation—is the dominant factor in determining the pattern and geometry of the LIPSS.

Short-pulsed laser in the fabrication of fine periodic surface structures (hereinafter, referred to as LIPSS: laser induced periodic surface structures) has been studied to reduce friction, improve control of wettability and improve bioaffinity. While it has low cost and stable irradiation compared with the ultrashort-pulsed laser traditionally used, it is difficult to control the fabrication of LIPSS using the short-pulsed laser because of its lower peak fluence than the ultrashort-pulsed laser and the unclarified principle. Optimizing the surface shape before laser irradiation may make it easier to control fabrication using short-pulsed laser since it has been reported that LIPSS is fabricated due to surface plasmons induced by plasma waves after altering the surface roughness during laser irradiation. The proposed method involves cutting the surface to assist with the short-pulsed laser for the control LIPSS: the surface of the workpiece is irradiated after straight microgrooves are fabricated by ultraprecision cutting. The experimental results showed that microgrooves made straight LIPSS with a high aspect ratio and also expanded the effective fluence range of experimental conditions when fabricating LIPSS. The new method was shown to control LIPSS effectively, and highlights the importance of the surface shape before laser irradiation for LIPSS fabrication.

Fine structures provide materials with various functionalities such as friction reduction and water repellency. A short-pulsed laser is a suitable method to effectively fabricate fine structures through self-organization, called as LIPSS (laser induced periodic structures). However, this method has difficulty in control of LIPSS since the principles and the phenomena have not been clarified completely. It has been reported that LIPSS follow debris on a material surface, hence, the short-pulsed laser assisted by mechanical processing was proposed, and the straightness and the aspect ratio of LIPSS were improved by laser irradiation on the surface with the straight microgooves. The short-pulsed laser assisted by mechanical processing was developed to control LIPSS and fabricate zigzag LIPSS, and the effects of the surface geometry before laser irradiation on LIPSS were investigated. Firstly, laser irradiation was conducted on the microgrooved surfaces with changing the angle of laser polarization to investigate the effects of the angle between groove direction and laser polarization on LIPSS. When the angle were from 45° to 90°, LIPSS followed the microgrooves regardless of the laser polarization. Based on the results, the laser was irradiated on the surfaces with zigzag microgrooves created by ultraprecision cutting, and zigzag LIPSS were fabricated as following zigzag microgrooves under the proper conditions. This study demonstrated the importance of the initial surface shape and the effectiveness of the short-pulsed laser assisted by mechanical machining to control LIPSS freely since the surface plasma waves are propagated from unevenness on the material surface.

Functional surface creation technologies have garnered increasing attention over the years. These technologies can provide various functions to a material by establishing a fine structure on the material surface and responding to the needs of industrial products with distinguished functions or high values. In addition, by creating a “composite fine structure,” which is composed of two kinds of structures with different scales, the enhancement of functions and emergence of new functionalities can be expected. Hence, our study combined a micrometer-scale V-shaped groove structure using an ultra-precision cutting and nanometer-scale ultra-fine periodic structure (LIPSS) using a short-pulsed laser. Then, we clarified the creation principle and studied the functionality of the structure, specifically, its wettability. As a result, it was found that optical behavior inside the V-shaped groove changed; therefore, the composite structure changed depending on the groove angle, laser polarization direction, and number of times of irradiation. In addition, it was found that the water wettability changed depending on the type of formed micro-nano composite structures. Moreover, the wettability could be controlled by depending on how the structure is used.

In recent years, nanostructures have been required for industry and medical services, to perform functions such as reduction in friction, control of wettability, and enhancement in biological affinity. Ultrashort pulsed lasers have been applied to meet these demands, and have been actively studied both experimentally and theoretically in terms of phenomena and principles. In this study, to clarify the phenomenon of the fabrication of laser-induced periodic surface structures (LIPSS), and its application to industry, experiments were conducted on SUS304, titanium, and nickel-phosphorus by a short pulsed laser that has a longer pulse duration, higher cost-effectiveness, and higher stability than ultrashort pulsed lasers. The results confirmed that while LIPSS were fabricated on Ti and Ni-P workpieces, a uniform fine periodic structure was not fabricated on the whole irradiated surface of SUS304, and crystal grain boundaries appeared with low energy density and irradiation number because SUS304 is an alloy composed of Fe, Cr, and Ni. Further, the short pulsed laser has a low power and long pulse duration, inducing the thermal effect. We clarified the effect of crystal structure on fabricating fine periodic surface structures with short pulsed laser.

Non-photorealistic rendering (NPR) can use various parameters and techniques to automatically generate a wide range of images with different painterly appearances. However, a real painting is the result of a creative process, and traditionally, many artists have developed their own media, styles, and techniques. Fortunately, the computer can also be used in different ways, for instance, as a tool to support and enhance creativity. We propose a system to interactively generate a painterly image through a suggestive interface. After the artist intuitively selects a region, our system immediately offers different suggestions of NPR modifications. The multidimensional NPR parameter space is transformed in a more perceptual space by optimization, which is validated by a user study. The suggested images generated from sampled parametric variations are displayed according to our perceptual distance. Through the same interface, our system allows for refinement or exploration without any need to understand the various parameters involved in generating NPR effects. The interest of our suggestive interface is supported by another user study, where participants felt that it stimulated their creativity as they interactively and iteratively created painterly images by choosing suggested images for the selected regions. Another experiment showed that different viewers found the resulting images more creative than their initial automatically generated images.

We propose a real-time rendering method of Japanese ink painting. Especially, we focus on methods both "mokkotsu" and "horinuri" techniques. We developed a real-time rendering system which can render Japanese ink painting images based on two techniques.

Ultrashort-pulsed laser irradiation is a more efficient approach to the fabrication of fine surface structures than traditional processing methods. However, it has some problems: the equipment expenses usually increase as the pulse shortens, and the process principle has not been clarified completely, although the collisional relaxation time (CRT) is assumed to be a major factor. In this study, a 20-ps pulsed laser was employed to fabricate nanometer-sized periodic structures on a stainless steel alloy, SUS304. The pitch length of the fabricated fine periodic structures was similar to the laser wavelength, and the results suggested that periodic structures could be fabricated within a limited range of the laser fluence. In order to expand the effective fluence range (EFR) and to control the pitch length, laser irradiation was carried out with different workpiece temperatures and the laser wavelengths. In this way, CRT was extended and EFR was expanded by cooling the workpiece, and the pitch lengths were approximately equal to the laser wavelengths. As a result, two things were found: it is easier to fabricate the fine periodic structures by cooling the workpiece, and it is possible to control the pitch length of the fine periodic structures by changing the laser wavelength.