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Femtosecond laser induced phenomena in glasses and photonic device applications Kazuyuki Hirao1, Yasuhiko Shimotsuma, Jianrong Qiu1 and Kiyotaka Miura1 Graduate School of Engineering, Kyoto University Nishikyo-ku, Kyoto 615-8510, JAPAN 1 Photon Craft Project, JST Keihanna Plaza, Seika-cho, Kyoto 619-0237, JAPAN ABSTRACT Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed inside glasses after the femtosecond laser irradiation. Here, we report the refractive index change, space-selective valence state manipulation of active ions, nano-grating and precipitation control of nanoparticles by a femtosecond laser in glasses. The mechanisms of the observed phenomena were also discussed. INTRODUCTION The history of glass spans four thousand years: as the oldest of man-made materials, it has permeated into every corner of our lives. However, the use of glass and ceramics for construction is only a small portion of its appeal. New attention is growing around the functional properties of glass materials. If the new glass boom of the eighties, when the functionality of glass was first explored, is thought of as the beginning of this movement, then the fusion of nanotechnology and glass to create nanotech-glass marks an entry into a new stage of development. The driving force that has sustained our lives has shifted from fire in ancient times, to heat, and then to electricity. In the 21st century, life will shift again into the age of light. The key to unlocking the new optical age is in glass nanotechnology including nano-ceramics. What if semiconductors were 1000 times faster, or were 1/1000 the size and price? What if optical discs could store 1000 times more information? What if glass could shine in any color we could imagine? What if plasma displays were 50% thinner? The answers to these questions are no longer merely dreams. These technologies may appear in the near future, thanks to the fusion of nanotechnology and glass: Nanotechnology Glass Project. The center of glass nanotechnology research in Japan is the Nanotechnology Glass Project, begun by NEDO as a five-year project to run from 2001 to 2005.The author has been appointed project leader, and Dr. Shuhei Tanaka (chief of R&D Department of NGF) and Dr. Junji Nishii (AIST KANSAI) have been named research leaders in Tsukuba and Osaka, respectively. Nanotechnology Glass Project is a new material created through nanotechnological processes, such as the dispersion of ions and infinitesimal particles within the glass, irradiation with short laser pulses, and super-fine processing, that allows for control and expression of functions and properties and structure at the molecular and atomic level. These are made possible by the full use of glass’ ease of processing and high compatibi