| It is an effective way to obtain visible and ultraviolet lights by using the laser passing through anisotropic medium such as LiB3O5(LBO),Ba B2O4(BBO),Bi B3O6(BIBO),KTi OPO4(KTP),KH2PO4(KDP),etc nonlinear optical(NLO)crystals.The breakthrough point of this technology is to prepare the NLO crystals with strong nonlinear response firstly,and further to improve the application range and laser conversion efficiency by properly adjusting the device design parameters.Re Ca4O(BO3)3(Re COB,Re:Y,Gd,La,Tm,Sm,etc.)crystals could be prepared by Czochralski method quickly.They had the advantages of the moderate birefringence,large effective NLO coefficient(deff),stable basic properties,large volume and high optical quality.They could also be easy to be doped with Re3+(such as Nd3+and Yb3+)ions as the laser crystals(such as Nd:Gd COB and Yb:YCOB).Therefore,the Re COB series crystals were a kind of ideal composite functional crystals.This paper is based on the development trend of the crystal lasers and NLO.The point of this paper is to study the optical properties of several Re COB crystals such as the TmCOB,RexGd1-xCOB(Re:Tm/Nd)and 0.5 at.%Nd:LaCOB.And the gain is to explore the application prospects of these crystals,the aim is to expand the output wavelength range of the crystal lasers,improve the output energy of lasers and achieve high efficiency frequency conversion.By means of experimental tests and theoretical calculations,the SHG properties of TmCOB,the NCPM properties of RexGd1-xCOB,and the spectral properties of 0.5 at.%Nd:LaCOB were studied.For TmCOB,the NLO coefficients(dij)were measured firstly.Then deff were calculated.Further,the type-II SHG properties of TmCOB at 1064 nm were investigated,which were also compared with the type-I situation.For RexGd1-xCOB(Re:Tm/Nd),the NCPM wavelengths of Tm0.02Gd0.98COB and Nd0.08Gd0.92COB were measured by experiments.The NCPM tunable waveband ranges of RexGd1-xCOB(Re:Tm/Nd,0<x<1)were summarized.And the SHG conversion efficiencies were measured by experiments.For 0.5 at.%Nd:LaCOB crystal,the absorption and fluorescence em ission spectra of this crystal were measured,and then they were analyzed by using J-O theory.The results of the above studies could provide the reference for evaluating whether the crystals investigated in this paper would be the excellent laser and NLO crystals.The results of the above studies showed that TmCOB,RexGd1-xCOB(Re:Tm/Nd)and0.5 at.%Nd:LaCOB crystals could be used in laser and nonlinear optics fields.For part 1,the NLO coefficients(dij)of TmCOB were measured by Maker fringe method firstly.The values of d11,d12,d13,d31,d32 and d33 were determined to be 0.19,0.26,-0.61,-0.30,1.66 and-1.25 pm/V,respectively.Then,the distribution of deff of the crystal was obtained.According to the deff,the optimal type-II PM direction was(118.0°,77.2°).The SHG efficiencies of the TmCOB crystal samples were tested under the Nd:YAG laser(40 ps,10 Hz).It was founded that the SHG conversion efficiency of TmCOB with 12 mm crystal processed along the optimal phase matching direction reached 55.90%under the fundamental lights energy of 6.89 m J.At the same time,the output energy was 3.85 m J.It could also be found that the angular acceptance of type-II PM was larger than that of type-I(8.0 times times of type-I values),and the walk-off angle for type-II PM was smaller than that of type-I(0.35 times of type-I values).For part 2,the NCPM wavelength of several Re1xRe21-xCOB mixed crystals(Tm0.02Gd0.98COB,Nd0.08Gd0.92COB,Lu0.129Gd0.871COB,Lu0.07Gd0.93COB and Sc0.04Gd0.96COB)were expolored by experimental measurements and theoretical calculations.Then the relationship between the radius of rare earth cations and the NCPM wavelengths of Re1xRe21-xCOB mixed crystals was summarized.The NCPM wavelengths of Tm0.02Gd0.98COB and Nd0.08Gd0.92COB were obtained by experimental measurements.And the actual NCPM tunable bands of TmxGd1-xCOB and NdxGd1-xCOB were determined.For Y-axis of TmxGd1-xCOB crystals,they had not practical type-I NCPM tunable band,and the type-II NCPM band was 1011-1022 nm.The type-I NCPM band of TmxGd1-xCOB along Z-axis was 839-884nm.The type-I and type-II NCPM bands of NdxGd1-xCOB along Y-axis were 831-927 nm and1255-1426 nm,respectively.The type-I NCPM band of NdxGd1-xCOB along Z-axis was 973-986nm.Finally,the conversion efficiency of Nd0.08Gd0.92COB with 16 mm reached 37.40%pumped by the fundamental light power of 1052 m W(Ti:sapphire laser,837 nm,120 fs,76 MHz).For part 3,by measuring the absorption spectra,fluorescence emission spectra and fluorescence attenuation curve of 0.5 at.%Nd:LaCOB crystal,the properties of absorption and fluorescence emission spectra could be studied by J-O theory.The crystal field parameters in different polarization directions were calculated by the least square method.Some conclusions could be got through theoretical calculations,that the maximum absorption cross section of the crystal near 808 nm was 4.79×10-20cm2 in Y polarization direction,the maximum absorption cross sections in Z and X polarization directions were 4.24×10-20 cm2 and 4.10×10-20 cm2,respectively.The maximum fluorescence emission cross sections in three polarization directions were all located at 1060 nm.The maximum emission cross section in X polarization direction was11.15×10-20cm2,and the maximum emission cross sections in Y and Z polarization directions were 5.55×10-20cm2 and 4.95×10-20cm2,respectively.The maximum fluorescence branching ratio was 59.02%,the average radiation fluorescence lifetime was 327.20?s,and the fluorescence lifetime was 107.98?s. |
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