Patterning of non-linear optical crystals in glass by laser-induced crystallization

This paper reports recent progress in the patterning of non-linear optical crystals on the glass surface by laser irradiation. Two techniques for the writing of crystal lines have been developed, i.e., rare-earth (samarium) atom heat processing and transition metal atom heat processing, in which a continuous wave Nd:YAG laser (wavelength: λ.= 1064 nm) is irradiated to the glasses containing rare-earth (RE: Sm³⁺, Dy³⁺) ions or transition metal (TM: Ni²⁺, Fe²⁺, V⁴⁺) ions. The writing of crystal lines such as ß-BaB₂O₄, Sm _xBi_1-xBO₃, and Ba₂TiGe ₂O₈ showing second harmonic generations has been successful. It is clarified from the azimuthal dependence of second harmonic intensity and polarized micro-Raman scattering spectra that crystal Unes consist of highly oriented crystals along the crystal line growth direction. It is also possible to write two-dimensional crystal bending or curved lines by just changing the laser scanning direction. The mechanism of the laser-induced crystallization has been proposed.