β-BaB2O4 with special cut-angle applied to single crystal cascaded third-harmonic generation**Project supported by the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR2017MF031 and ZR2018BF029).

Abstract

High-efficiency single crystal cascaded third-harmonic generation (THG) was realized in β-BaB2O4 (BBO) material with special cut-angle. By analyzing effective nonlinear optical coefficient (deff) of the cascaded THG process, which was composed by type-II frequency doubling and type-I sum-frequency, the optimum phase matching (PM) direction in BBO crystal was determined to be (θ = 32.1°, ϕ = 11°). With an optimized 9-mm long sample which was processed along this direction, the highest cascaded THG conversion efficiency reached 42.3%, which is much superior to the similar components reported previously, including ADP, KDP, and GdxY1−xCOB crystals.