Laser-Induced Line Patterning of Nonlinear Optical Crystals in Glass

This paper reports the progress in the patterning of nonlinear optical crystal lines on a glass surface by laser irradiation techniques. Two techniques for the patterning of crystal lines have been developed, i.e., rare-earth atom heat processing and transition metal atom heat processing, in which continuous-wave lasers such as Nd:YAG laser (wavelength: lambda = 1064 nm) are irradiated onto the glasses containing rare-earth ions such as Sm³⁺ and Dy³⁺ or transition metal ions such as Ni²⁺ and Cu²⁺. The patterning of lines consisting of nonlinear optical crystals such as beta-BaB₂O₄, SmxBi_1- xBO₃, (Sr,Ba)Nb₂O₆, and LiNbO₃ has been achieved. It is clarified from the azimuthal dependence of second harmonic intensities and polarized micro-Raman scattering spectra that nonlinear optical crystals in the lines are highly oriented along the laser scanning direction, i.e., the patterning of single-like crystal lines. It is also possible to pattern two-dimensional crystal bending or curved lines by just changing the laser scanning direction, and such bending crystal lines have a potential for optical waveguides.