High-density bump formation on a glass surface using femtosecond laser processing in water

Micrometer-sized bumps were formed on a glass surface using a focused femtosecond laser processing in water. The bumps were formed over a wide ranges of pulse irradiation parameters, including irradiation energy and focus position. The bumps exhibited a wide variety of morphologies and sizes depending on the parameters. The use of a liquid, namely heavy water, which returns after breakdown and cavitation bubble formation, enabled us to fabricate bumps with high spatial density, which is not possible using a solid coating that is ablated. A desired arrangement of bumps on a glass surface was fabricated by tuning the processing time interval to be more than the disappearance time of a bubble, generated by focusing a femtosecond laser pulse near the water/glass interface. PACS 42.62.Cf; 42.70.Ce; 52.38.Mf; 78.47.+p; 79.20.Ds