Some glasses such as 21.25 Sm2 O3. 63.75Mo O3. 15 B2 O3 (mol %) giving the formation of nonlinear optical Sm2 (Mo O4) 3 crystals through conventional crystallization in an electric furnace and through continuous-wave Nd: yttrium aluminum garnet (YAG) laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) have been developed. It is proposed from x-ray diffraction analyses, micro-Raman-scattering spectra, and second-harmonic generation measurements that the crystal structure of Sm2 (Mo O4) 3 formed by the crystallization is the ß′ -phase structure with an orthorhombic (noncentrosymmetric) symmetry. The lines consisting of nonlinear optical ß′ - Sm2 (Mo O4) 3 crystals are written at the surface of glasses by YAG laser irradiation (laser power: P=0.4 W, laser scanning speed: S=1-10 μms), and, in particular, homogeneous crystal lines are formed at the laser scanning speed of 1 μms. Refractive index changes (not crystallization) are also induced by YAG laser irradiation of P=0.4 W and a high laser scanning speed of S=25 μms. The crystallization mechanism in the laser-irradiated region has been proposed. The present study demonstrates that the samarium atom heat processing is a technique for the writing of rare earth containing optical nonlinear/ferroelectric crystal lines in glass.