Defocused CO$_2$ laser beam irradiation strengthening of 60kgf/$\textrm{mm}^2$ grade steel sheet was investigated to obtain the tensile strength similar to that of fully penetrated one by the focused beam. The melted line width by the defocused beam was 3∼4 times larger compared to that of the focused beam. However, the increase of tensile strength with 1 line irradiation by the defocused beam was similar to that of 2~3 lines by the focused beam. The increase(37.6%) of bending strength with 1 line by the defocused beam was higher than the increase(12.9%) of tensile strength. Also, the effect of cooling gas to strengthening was observed.

Due to the heat confinement in the shallow region of the target for a short time scale, pulsed laser annealing has received an increasing interest for the fabrication of poly-Si thin film transistors(TFTs) on glass as a low cost substrate in the flat panel displays. The formation and growth mechanisms of poly silicon(poly-Si) grains in thin films are investigated using an excimer laser crystallization system. To understand the crystallization mechanism, the grain formations are observed by FESEM photography. The optical reflectance and transmittance during the crystallization process are measured using HeNe laser optics. A two-step ELC(Excimer Laser Crystallization) process is applied to enhance the grain formation uniformity.

6061 aluminum alloy sheets were I-square butt welded using a continuous wave Nd:YAC laser. Heat inputs were varied from 54.6 to 80 J/mm for butt welding using different sets of the laser power and the weld speed. I-square butt welds were also made with and without Ar shielding gas. The effect of Ar shielding gas and heat input on the mechanical properties and formability was investigated using Vickers hardness, transverse-weld tensile and bulge test. Porosity on the weld beads and sections and hot crack on the fracture surfaces of transverse-weld tensile test specimens were investigated using optical and scanning electron microscopy The experimental results showed that mechanical properties and formability of 6061 aluminum alloy laser welds were degraded compared to those of base metal. Mechanical properties and formability of 6061 aluminum alloy laser welds were not substantially changed when Ar shielding gas was supplied or heat inputs were varied.

A laser shock cleaning technology is a new dry cleaning methodology for the effective removal of small particles from the surface. This technique uses a plasma shock wave produced by a breakdown of air due to an intense laser pulse. In order to optimize the laser shock cleaning process, it needs to evaluate the cleaning performance quantitatively by using a monitoring technique. In this paper, an acoustic monitoring technique was attempted to investigate the laser shock cleaning process with an aim to optimize the cleaning process. A wide-band microphone with high sensitivity was utilized to detect acoustic signals during the cleaning process. It was found that the intensity of the shock wave was strongly dependent on the power density of laser beam and the gas species at the laser beam focus. As a power density was larger, the shock wave became stronger. It was also seen that the shock wave became stronger in the case of Ar gas compared with air and N$_2$ gas.

In this study, manufacturing of polymer master and mold insert for micro injection molding was investigated. Ablation by excimer laser radiation could be used successfully to make 3-D microstructure of PET. The mechanism for ablative decomposition of PET with KrF excimer laser(λ: 248nm, pulse duration: 5ns) was explained by photochemical process. And this process showed PET to be adopted in polymer master for nickel mold insert. Nickel electroforming by using laser ablated PET master was preferable for replication method. Finally, it was shown that excimer laser ablation can substitute for X-ray lithography of LIGA process in microstructuring.