| Frequency up-conversion technology is not only an important branch in nonlinear optics,but also an efficient approach for visible and ultraviolet(UV)lasers.By means of NLO crystals with excellent properties and scientific optical path design,using phase-matching technology,near-infrared(NIR)lasers can be changed to visible and UV wavebands,even vacuum UV,which satisfy the demands in different fields.In this dissertation,the technologies of polycrystalline materials synthesis and single crystal growth of RECa4O(BO3)3 type crystals were explored.For the first time,LaxY1-xCOB series crystals with different compositions were designed and grown by the conventional Czochralski(Cz)pulling method.By analyzing the crystal structures of LaxY1-xCOB crystals,the influence from the substitution of Y3+ ions in YCOB crystal with La3+ ions on crystal structures and optical properties was dicussed,and the non-critical phase-matching(NCPM)properties of LaxY1-xCOB crystals were further studied.In order to achieve NCPM frequency conversions of an Nd:glass laser(1053 nm),a series of GdxY1-xCOB crystals has been grown,correspondingly,the 1053 nm NCPM type-? second-harmonic-generation(SHG)and type-I third-harmonic-generation(THG)properties of GdxY1-xCOB crystals were investigated.Based on the characteristics for changing the laser polarization of wave plates,utilizing the special NCPM properties of GdxY1-xCOB crystals,we designed and realized a novel single crystal cascaded THG converter.Then,KDP and ADP crystals were applied in this converter,and efficient THG outputs of 1064 nm were obtained.The main work and results are as follows:Based on the growth experience and previously theoretical studies of RECOB series crystals,the initial crystal components of LaxY1-xCOB and GdxY1-xCOB crystals were designed.According to the chemical formulas and stoichiometric ratios of the compositions of the designed LaxY1-xCOB and GdxY1-xCOB crystals,the raw materials were weighted.Then by employing the polycrystalline preparation technology,LaxY1-xCOB and GdxY1-xCOB polycrystalline materials were systhesized by solid-state reactions.By optimizing the single-crystal-growth parameters and utilizing the<010>-orientated YCOB crystal seed,LaxY1-xCOB and GdxY1-xCOB series crystals with large size and high optical quality were prepared.All the as-grown crystals possessed large size with dimensions of 20 mm-25 mm in diameter and 25 mm-40 mm in length.The real chemical compositions of the as-grown GdxY1-xCOB and GdxY1-xCOB crystals with different compositions were determined by using X-ray fluorescence analysis(XRF).The XRF results showed that the La contents in the seven different GdxY1-xCOB crystals were 0.151,0.140,0.124,0.120,0.104,0.096,and 0.089,respectively,and the Gd concentrations in the four different GdxY1-xCOB crystals were 0.186,0.156,0.132,and 0.127,respectively.The segregated test results indicated that the La ions were relative harder than Gd ions to incorporate into the YCOB crystal lattice.The crystal structure,structure-property relationships and NCPM properties of GdxY1-xCOB series crystals were investigated for the first time.By replacing the Y3+ions in YCOB crystal with La3+ ions that possess larger ionic radius,several GdxY1-xCOB crystals with different La/Y ratios were grown.X-ray powder diffraction and single-crystal X-ray diffraction experimental results proved that all these crystals have formed in GdxY1-xCOB substitutional solid solution,and possess the same symmetry(space group Cm)as YCOB.Taking advantage of the OPO laser,the NCPM type-? SHG and type-?THG wavelengths along the Y-axis were determined for different?GdxY1-xCOB crystals at room temperature,correspondingly,the dependence of the NCPM wavelength on the compositional parameter x was given out.According to the results of crystal structure analyses and NCPM wavelength measurements,the relationships between and among the optical birefringence,NCPM wavelength and crystal structure were revealed,where the NCPM wavelength is believed to be associated with the cell parameter ratio a/c.Using a 1064 nm Nd:YAG laser as the fundamental light source,by controlling the crystal temperature,NCPM SHG and THG of the 1064 nm laser were realized from different GdxY1-xCOB crystals.Utilizing the La0.120Y0.880COB crystal,a type-? NCPM SHG of 1064 nm was achieved at 30?,giving out a temperature acceptance bandwidth of 38.4?·cm,an angular acceptance bandwidth of 155.9 mrad cm1/2,and an optical conversion efficiency of 48.8%.With the La0.140Y0.860COB crystal,a type-I NCPM THG of 1064 nm was realized at 50?,and the temperature acceptance bandwidth,angular acceptance bandwidth,and optical conversion efficiency were obtained to be on the order of 31.8?·cm,219(??L/1/2)mrad·cm1/2 and 118(??L1/2)mrad·cm1/2,and 32.4%,respectively.At last,we discussed the mechanism and solutions of the THG-induced gray-track in La0.140Y0.860COB crystal during the THG experiments.We investigated the 1053 nm NCPM SHG and THG properties of GdxY1-xCOBcrystals systematically.By adjusting the compositional parameter x,we designed and grew four GdxY1-xCOB crystals with different compositions.Using an optical parametric oscillator(OPO)laser,the type-? NCPM SHG and type-I NCPM THG wavelengths along the Y-axis for different GdxY1-xCOB crystals were measured at room temperature and the compositions for NCPM SHG and THG of a 1053 nm laser were determined.By using a 1053 nm Nd:YLF laser as the fundamental light source,the NCPM properties were investigated.With the Gd0.132Y0.868COB crystal,a type-?NCPM SHG of 1053 nm was achieved at 28?,giving out a temperature acceptance bandwidth of 43.5?·cm,an angular acceptance bandwidth of 162 mrad,cm1/2,and an optical conversion efficiency of 44%.With the same crystal,a type-I NCPM THG of 1053 nm was achieved at 55?,and the corresponding temperature acceptance bandwidth,angular acceptance bandwidth,and optical conversion efficiency were 29?·cm,204(??LL/12)and 117(??L1/2)mrad·cm1/2,and 29.8%,respectively.Similar to GdxY1-xCOB crystal,the THG-induced gray-track in Gd0.232Y0.868COB crystal during the 1053 nm THG experiments was removed by elevating the crystal temperature and the gray-track forming reason was analyzed.Then,the solution for inproving the THG energy and conversion efficiency without the formation of gray-track was put forward.A novel single crystal cascaded THG converter based on the birefringent phase-matching(BPM)properties was designed and demonstrated.The frequency conversion output from the NIR to the UV was realized with one crystal as the core component,at the same time,it is the first time that the cascaded frequency up-conversion processes are realized in one bulk NLO crystal.According to the special relationships between the component x and the corresponding NCPM wavelength of GdxY1-xCOB crystals,utilizing a quarter-wave plate of 2co wavelength to adjust the polarization of the SHG wave and a round-trip optical path to realize the SHG and SFG processes,THG outputs of 1064 nm and 1053 nm lasers with ultra-wide angular acceptance were obtained from one GdxY1-xCOB crystal and the conversion efficiencies were 2.3%and 1.8%,respectively.Then,KDP and ADP crystals were applied in this specially designed optical structure,and efficient THG outputs were obtained.Using a 1064 nm,40 ps pulse laser as the fundamental light source,the maximum THG output at 355 nm was 1.13 mJ,and the highest THG conversion efficiency was 30.7%for KDP crystal;the maximum THG output was 1.61 mJ,and the highest conversion efficiency from 1064 nm to 355 nm was 35%for ADP crystal.The further theoretical analyses indicate that this THG converting style of KDP and ADP crystals is applicable for various fundamental wavelengths at 1?1.1 ?m range.Compared to the widely used traditional cascaded THG converters which require two NLO crystals,this component keeps high efficiency and high damage threshold,at the same time,its production cost is reduced.In addition,such design can be applied to other cascaded frequency up-conversion processes,or other NLO crystals such as DKDP,DADP,BBO and BIBO etc,as long as the related cascaded frequency up-conversions have similar BPM angles.This technique enriches the design concepts of NLO components,and it is anticipated to be applied in practice in the near future. |
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