Several plastics subjected to femtosecond laser irradiation were first studied concerning surface roughness and wettability.Femtosecond laser irradiation could easily control the wettability and the surface free energy, and their variations depended on the polarity of the plastics. Next, the effects of shapes and chemical states on the wettability of plastic surfaces were investigated. Regardless of the plastic polarity, the contact angle of pure water changed continuously depending upon the surface roughness. On the other hand, there was no correlation between the contact angle and chemical state. It was revealed that from these results that the change of the wettability largely depended on the surface shape and could be controlled by laser irradiation.

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Ferrous soft magnetic materials are commonly used for electric facilities, and especially, electric steel sheet for motors has been growing in importance in all industries. In order to miniaturize and increase the efficiency of electric motor unit, the magnetic flux in steel sheets needs to be controlled and flux leakage to be cut off. In this work a unique laser working on thin steel sheet combining cutting and melt-infiltration has been examined as a possible processing for local non-magnetization in a shape of a narrow layer.
Two-ply 0.5 mm-thick steel sheets were cut using defocused laser beam so as to make 0.2～ 0.8 mm-wide slit. The cut surface exhibited metallic luster and little oxidation. Then Cu or Cu-Si wire was placed onto a slit and melted using 1.0～ 4.0 kW laser beams. Due to a low laser absorptance of copper, more than 2.0 kW-laser power was needed to infiltrate the Cu completely, which caused a melting of the adjacent edges of steel slits with considerable dissolution of Fe into a Cu infiltration.
The Cu-Si wire showed a deeper infiltration than pure Cu wire. The magnetic flux density across the infiltration-modified layers decreased linearly with decreasing the amount of Fe dissolution. Under the best process conditions, it was decreased by 64% compared with an unmodified material, which reveals a modified emissivity less than 1/10 of electric steel sheet.

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