Deep-ultraviolet nonlinear-optical crystal BaNa_(2)PO_(3)(OH)_(2) with large birefringence and strong second-harmonic-generation response

摘要

Deep-ultraviolet(DUV,λ<200 nm)nonlinear-optical(NLO)crystals play a pivotal role in modern laser science and technology.Metal phosphates have been considered as fascinating candidates for DUV NLO crystal material.However,how to generate both strong second-harmonic-generation(SHG)response and large birefringence for promising DUV NLO metal phosphates is a long-standing issue.Herein,a new DUV NLO metal phosphate,BaNa_(2)[PO_(3)(OH)]_(2),was successfully synthesized,which features a two-dimensional[NaPO_(3)(OH)]_(∞)alveolate layer alternately connected by highly asymmetric[PO_(3)(OH)]groups and NaO5 triangular bipyramids.BaNa_(2)[PO_(3)(OH)]_(2)can realize a good balance of DUV nonlinear properties covering short UV absorption edge less than 190 nm,strong SHG response with the magnitude of~1.2×benchmark KH_(2)PO_(4)(KDP),and the largest birefringence with the experimental value of 0.064@590±3 nm in reported alkaline/alkaline-earth metal phosphates,producing the shortest phase-matching output down to the wavelength of 164 nm.These research results show that BaNa_(2)[PO_(3)(OH)]_(2)crystal is a potential DUV NLO crystal material.