Two-dimensional Raman imaging for periodic domain structures in laser-patterned ferroelastic β′-(Sm,Gd)2(MoO4)3 crystal lines in glass

Ferroelastic β′-(Sm,Gd)2(MoO4)3, (SGMO), crystal lines are patterned on the surface of Sm2O3–Gd2O3–MoO3–B2O3 glasses by continuous-wave Yb:YVO4 laser irradiations (wavelength: 1080 nm, power: 1.2 W, scanning speeds: 4–7 μm/s), and the structure of periodic domains self-organized in the crystal lines is examined from two-dimensional micro-Raman scattering spectrum imaging. It is found that the periodicity in the domain structures with different refractive indices changes depending on the laser scanning speed, i.e., on the growth rate of SGMO crystals. It is proposed that the arrangements of (MoO4)2− tetrahedra giving the antisymmetric Mo–O stretching vibrations in SGMO crystals changes along the crystal growth direction (i.e., along the line) gradually and periodically due to spontaneous strains. The present study suggests that the appearance of periodic domain structures and second harmonic intensities is an intrinsic feature in the laser patterning of ferroelastic β′-(Sm,Gd)2(MoO4)3 crystals.