Laser-assisted direct roller imprinting of large-area microstructured optical surfaces.

In this study, a high-throughput fabrication method called laser-assisted direct roller imprinting (LADRI) was developed to lower the cost of nanoimprinting large-area polymer films and to address problems associated with nanoimprinting, namely, microstructural damage and precision in flatness of entire film. With LADRI, the laser directly heats the microstructured surface of the roller mold, which heats and melts the surface of a polymethyl methacrylate (PMMA) film to replicate the microstructures on the mold rapidly. In this study, the effects of laser power density, scanning speed, size of the microstructures, and contact pressure on the replication speed were investigated experimentally.

Mechanism and performance evaluation of transient and selective laser processing of glass based on optical monitoring.

Femtosecond laser processing has been widely applied in glass processing owing to its ability to fabricate microscale components. To improve processing efficiency, a transient and selective laser (TSL) processing technique was previously developed, in which electron excitation was induced inside a transparent medium by a single pulse of femtosecond (fs) laser, and a single pulse of microsecond (µs) laser can be selectively absorbed in this excited region to heat and remove the material. However, because of its high speed removal process, the unclear mechanism and inefficient evaluation of its processing performance limit its further application.

Quantitative Description of Bubble Formation in Response to Electrolyte Engineering.

The green hydrogen economy is expected to play a crucial role in carbon neutrality, but industrial-scale water electrolysis requires improvements in efficiency, operation costs, and capital costs before broad deployment. Electrolysis operates at a high current density and involves the substantial formation of gaseous products from the electrode surfaces to the electrolyte, which may lead to additional resistance and a resulting loss of efficiency. A detailed clarification of the bubble departure phenomena against the electrode surface and the surrounding electrolytes is needed to further control bubbles in a water electrolyzer.

High-speed microgroove processing of glass by expanding the high-temperature region formed by transient and selective laser absorption.

Microgroove processing of glass is important in many fields, however, it is difficult to achieve the processing with a high speed. In this study, we developed a novel method for the high-speed microgroove processing of glass using two types of lasers, namely a femtosecond laser and a near-infrared continuous-wave (CW) laser. A single femtosecond laser pulse was initially focused on the surface of the material, enabling the area to absorb the CW laser, which is otherwise not absorbed by the glass.

Sample-efficient parameter exploration of the powder film drying process using experiment-based Bayesian optimization.

Parameter optimization is a long-standing challenge in various production processes. Particularly, powder film forming processes entail multiscale and multiphysical phenomena, each of which is usually controlled by a combination of several parameters. Therefore, it is difficult to optimize the parameters either by numerical-model-based analysis or by "brute force" experiment-based exploration.

Ultrafast internal modification of glass by selective absorption of a continuous-wave laser into excited electrons.

The internal modification of glass using ultrashort pulse lasers has been attracting attention in a wide range of applications. However, the remarkably low processing speed has impeded its use in the industry. In this study, we achieved ultrafast internal modification of glass by coaxially focusing a single-pulse femtosecond laser and continuous-wave (CW) laser with the wavelength that is transparent to the glass.

Simulation of ultrashort pulse laser drilling of glass considering heat accumulation.

In accordance with the increasing demand for high-speed processing, the repetition rate of ultrashort pulse lasers has continued to increase. With the development of these lasers, there is a growing demand for the prediction of shapes processed at high repetition rates. However, the prediction of these shapes is a major challenge, because of the difficulty associated with the estimation of heat accumulation.

Dynamics of pressure waves during femtosecond laser processing of glass.

Although femtosecond lasers enable microfabrication of transparent materials, precise processing is difficult owing to the inevitable damage caused to the surroundings of the processed region. In the present work, we combine pump-probe imaging with a high-speed camera to capture the dynamics of pressure waves varying from pulse to pulse, before a desired shape is created by hundreds of pulses. The results demonstrate that the pressure waves change their forms and locations as the number of pulses increases.

Laser-Assisted Thermal Imprinting of Microlens Arrays-Effects of Pressing Pressure and Pattern Size.

Polymer films with nano- or microstructured surfaces have been widely applied to optical devices, bioplates, and printed electronics. Laser-assisted thermal imprinting (LATI), in which a laser directly heats the surfaces of a mold and a thermoplastic polymer, is one of the high-throughput methods of replicating nano- or microstructures on polymer films. Only the surfaces of the mold and polymer film are heated and cooled rapidly, therefore it is possible to replicate nano- or microstructures on polymer films more rapidly than by using conventional thermal nanoimprinting.