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: Sm 3+ , Dy 3+ ) ions or transition metal (TM: Ni 2+ , Fe 2+ , V 4+ ) ions. The writing of crystal lines such as β‐BaB 2 O 4 , Sm x Bi 1− x BO 3 , and Ba 2 TiGe 2 O 8 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 lines 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.