Study On Second Harmonic Generation And Third Harmonic Generation Based On A New Nonlinear Optical Crystal Ba₃(ZnB₅O₁₀)PO₄（BZBP）

Laser is an artificial electromagnetic wave amplified by stimulated emission of radiation.With characteristics such as high power density,monochromaticity,directionality and coherence,laser is widely used in medicine,communication,industry,biology,military,scientific research and other fields.With the wide application of laser,higher requirements are put on laser output wavelength.The frequency conversion technology based on nonlinear optical crystals can be used to effectively extend the output wavelength range（ultraviolet and infrared ranges）of existing lasers.Therefore,the exploration of new nonlinear optical crystal materials has been one of the research hotspots in the field of nonlinear optics.In this paper,a new nonlinear optical crystal Ba₃(ZnB₅O₁₀)PO₄was grown,and then its basic physical properties were characterized,and phase matching range was calculated theoretically.Finally,the second harmonic generation（SHG）and third harmonic generation（THG）laser outputs were realized.The main research contents are as follows:（1）Characterization and analysis of the physical and optical properties of Ba₃(ZnB₅O₁₀)PO₄crystal.The BZBP single crystals were obtained by Top Seeded Solution Growth（TSSG）,and the crystal samples that could be used in the tests of physical and optical property of BZBP crystal were produced with the basic principles of crystal physics as the guide.The transmittance and weak absorption performance of BZBP crystal were conducted to determine the wavelength bands with practical application prospects.Then the variable temperature refractive index was tested,and the dispersion coefficient was fitted to provide the basis for the following theoretical calculation of phase matching.The Maker Fringe method test was conducted to obtain the nonlinear optical coefficients of BZBP.The damage threshold test was conducted,and the laser damage threshold of BZBP crystal was obtained,which was about 1.04GW/cm².Finally,the thermal expansion of the crystal was tested,and the thermal conductivity of the crystal was calculated.（2）Study on second harmonic generation performance of Ba₃(ZnB₅O₁₀)PO₄crystals.Based on the dispersion equation of BZBP crystal,the frequency doubling phase matching range was calculated theoretically.The phase matching angle of the crystal at 1064 nm wavelength ofθ=11.35°,?=0°,and the effective nonlinear coefficient d_eff=1.4 pm/V.The SHG experiment was conducted with OPO nanosecond laser.The results show that the SHG conversion efficiency of 35.4%.Based on the distribution of its effective nonlinear coefficient,the achieved maximum d_effvalue was 1.43 pm/V on the z-axis and 0.66 pm/V on the y-axis.The NCPM SHG range of wavelengths of BZBP crystal can achieve 740-780 nm on the y-axis,and 978-1056 nm on the z-axis.At 1012 nm（z-cut 3×3×5 mm³）and 750 nm（y-cut 5×5×13 mm³）to achieve the highest efficiency of NCPM SHG output,with efficiencies of 35%and 45.5%respectively.Further,the angular acceptance and spectral acceptance for non-critical phase matching were theoretically calculated.（3）Study on third harmonic generation performance of Ba₃(ZnB₅O₁₀)PO₄crystals.An effective third harmonic generation operation,produced by type-I phase-match in a 17.6 mm long BZBP nonlinear optical crystal was demonstrated.The BZBP has the NLO coefficients d₃₁=0.66 pm/V,d₃₃=0.65 pm/V,the type-I PM ofθ=90°,?=73.2°for THG 355 nm laser with the walk-off angle of 6.06 mrad,the angular acceptance of 66.3 mrad·mm and spectral acceptance of 2.59×10^-3μm·mm.Using nanosecond pulsed 1064 nm laser as pump source,the BZBP THG laser could be achieved the maximum conversion efficiency of 28.4%.