Laser fabrication of photorefractive Bragg reflectors, asymmetric waveguides and void arrays in glass

We have been studying the refractive index changes and vacancies that are induced in silica glass by the irradiation of ultrashort laser pulses. By scanning the laser beam in the glass we can form 3-D shape of waveguides, arrays of tiny vacancies, called voids, and long holes with microscopic diameters. In this paper, we report on the asymmetry of the waveguide formed by linearly polarized ultrashort pulses. The formation of the photo-induced waveguide is normally accompanied by the filamentation, the self-trapping of laser beam due to nonlinear optical effects. The asymmetric cross-section of the waveguide structures explains properly the illusory birefringence of photo-induced waveguides observed earlier. The cross-sectional forms of the waveguides were observed by polishing and etching the cross-psections. We also report the possibility of forming asymmetric shapes of voids. The asymmetry of voids results from the beam profile. We controlled the profile by inserting apertures before the focusing lens. The asymmetry leads to the polarization dependence of diffraction from the array of voids. We also report on the formation of Bragg grating in glass. The Bragg gratings were formed in soda-lime glass. We succeeded in forming a series of three Bragg gratings. The formation of grating inside glass was confirmed by diffraction experiments and chemical etching of polished cross-sections.