Anisotropic Raman spectral analysis and laser output based on large-sized scheelite bismuth molybdate tungstate mixed crystals

Abstract

Novel Raman crystals can significantly help to expand the available laser wavelength bands and effectively promote the development of laser technology. Bismuth molybdate and tungstate mixed crystals, Bi₂Mo_2.6W_0.4O₁₂ (BMO), with a scheelite crystal structure, are found to have superior Raman gain characteristics. Large-sized single crystals of BMO with dimensions up to 83 mm × 65 mm × 55 mm were sucessfully grown in the Bi₂O₃–MoO₃ hybrid-flux solutions by the top-seeded solution growth (TSSG) method. Spontaneous polarized Raman spectra of BMO crystals were systematically measured and analyzed based on microvibrations of the composing Raman active ionic groups. Through comparison, it was found that BMO crystals had a large Raman gain coefficient, 1.1 times that of the mostly used YVO₄ crystals. Besides, under the pump of a 1064 nm laser, a first-order Raman laser at 1176 nm, and dual-wavelength of both first-order and second-order at 1315 nm, were achieved under the Y(ZZ)Y and Y(XX)Y configurations, respectively. A maximum output power of 1.12 mW, corresponding to an optical-to-optical conversion efficiency of 15.6%, was successfully achieved. This work provides systematic analysis of the polarized Raman spectra of BMO crystals and reveals their great application prospects as novel Raman laser crystals.