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: k 5 1064 nm) is irradiated to the glasses containing rare-earth (RE: Sm 31 , Dy 31 ) ions or transition metal (TM: Ni 21 , Fe 21 , V 41 ) ions. The writing of crystal lines such as b-BaB 2 O 4 , Sm x Bi 1Àx 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. II. REAH/TMAH ProcessingIn rare-earth atom heat processing, cw Nd:YAG lasers with l 5 1064 nm are irradiated onto glasses containing Sm 2 O 3 (or M. Davies-contributing editor

Transparent crystallized glass with a surface crystallization layer of sub-millimeter thickness was found in the glass compositions of 35BaO15TiO 2 50GeO 2 (BTG50), 28BaO18TiO 2 54SiO 2 (BTS54), and 35SrO20TiO 2 45SiO 2 (STS45), and the precipitated fresnoite-type crystalline phase showed nonlinear optical properties. XRD

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Glass-ceramics (GCs) are materials obtained from the crystallisation of functional phases in glass, and have a structure that the crystallised phase embedded in the glass matrix. Glass-forming oxides are commonly added to the functional phases to improve the stability of precursor glass; however, the issue of glass-ceramics permitting the presence of residual phases resulting from addition is required to be clarified. To elucidate this issue, we prepared ‘perfectly surface-crystallised’ GC consisting of fresnoite-type Sr2TiSi2O8 from a non-stoichiometric glass and performed texture/morphology observations. Numerous SiO2-rich binodal-like nanospheres (~10 nm) were parasitic on the fresnoite single-crystal domains. The parasitic texture is considered to form via the following process: (i) binodal-type phase separation into stoichiometric fresnoite (crystalline matrix) and SiO2-rich phases (amorphous nanoparticles) and (ii) single-domain formation by surface crystallisation in the matrix. Furthermore, in terms of texture, the resulting GC differs from the GCs reported to date, i.e., inverse GC.

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