Synthesis and laser patterning of ferroelastic β′-RE2(MoO4)3 crystals (RE: Sm, Gd, Tb, Dy) in rare-earth molybdenum borate glasses

The glasses with the compositions of 22.5RE2O3–47.5MoO3–30B2O3 (RE: Sm, Gd, Tb, and Dy) (mol%) were prepared by a conventional melt quenching method, and the formation and laser patterning of ferroelastic β′-RE2(MoO4)3 crystals were examined. The initial crystalline phase was β′-RE2(MoO4)3 in all the glasses, and the second crystalline phases were rare-earth borates such as Gd(BO2)3, Tb(BO2)3, and DyBO3, and α-RE2(MoO4)3 in the glass with Sm2O3. It was confirmed from polarized optical microscope observations and micro-Raman scattering spectra that β′-RE2(MoO4)3 crystal lines having periodic refractive index changes were patterned by irradiations of continuous wave Yb:YVO4 fiber laser (wavelength:1080 nm, power: 0.5–2.0 W, scanning speed: 8–20 μm s−1). It was found that the periodic degree of refractive index changes depends on the kind of RE3+ ions. The present study demonstrates that the appearance of periodic domain structures is an intrinsic feature in the laser patterning of ferroelastic β′-RE2(MoO4)3 crystals.