Abstract
Recently, the structural modifications of glass by focusing femtosecond laser pulses have been demonstrated. We present photo-induced structural changes in silica glass with femtosecond laser pulses. We investigated the relationship between the formation of filaments and local refractive index changes in silica glass. In situ observation revealed the coincidence between the location of filament and that of refractive index change. The observation also showed that the region of refractive index change elongates toward the upstream direction of laser pulses with the exposure time. The region of refractive index change was several hundred- micron long and the diameter was smaller than two microns. The length of the region was dependent on the numerical aperture of focusing lenses. The refractive index change was confirmed to be as large as 0.01 by three different methods. We fabricated a 2-mm waveguide by translating the sample along the optical axis.
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