Laser patterning and characterization of optical active crystals in glasses

This paper reports the recent progress in the laser patterning of optical active crystals such as BaAlBO3F2 and β-BaB2O4 in glasses. In the laser-induced crystallization using continuous-wave lasers such as Yb:YVO4 fiber lasers (wavelength: 1080 nm), a steep temperature gradient is created in the laser-irradiated region, and highly oriented crystal lines are patterned at the glass surface. The quality and orientation of crystals patterned are characterized from the azimuthal dependence of second harmonic intensities, polarized micro-Raman scattering spectra, and transmission electron microscope observations. Two-dimensional planar crystals with high orientations are patterned by applying laser irradiations with large overlapping. The patterning of crystals in the inside of glass fibers is also possible by moving gradually laser focal point from the surface into the inside. The progress in the crystal patterning with desired morphologies and high orientations provides a high potential for optical active device applications.