| 题名 | Yb/Nd掺杂超快激光晶体的生长及性能研究 |
| 作者 | 李东振 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 夏长泰 |
| 关键词 | 激光晶体 提拉法生长 Yb:CaYAlO4 Nd:CaYAlO4 Nd:LSO Nd:LYSO Nd:GYSO Nd:LGSO |
| 其他题名 | Study of growth and properties of Yb/Nd doped ultrafast laser crystals |
| 中文摘要 | 开发新型高效率高功率全固态超快激光器具有重要意义，其中Yb3+和Nd3+掺杂的无序晶体材料越来越受到关注。CaYAlO4晶体为四方晶系，Ca2+和Y3+无序分布在AlO6八面体层中间；另外正硅酸盐晶体为单斜晶系，可为掺杂离子提供低对称性并且扭曲的晶格场，从而使得掺杂稀土离子光谱展宽，是超快激光晶体的理想基质。本论文重点选择Yb/Nd掺杂的CaYAlO4晶体和Nd掺杂的Lu2SiO5、LuYSiO5、GdYSiO5、LuGdSiO5晶体作为研究对象，对其提拉法晶体生长、晶体结构、热学性能、光谱性能及激光性能开展了探索性的研究工作，主要内容如下： 1. 采用提拉法生长出质量优异的Yb:CaYAlO4单晶。通过ICP-AES方法测试了Yb:CaYAlO4晶体中Yb3+的分凝系数为0.74，表明Yb3+在CaYAlO4基质中较易掺杂。通过XRD粉末衍射法测定了Yb:CaYAlO4晶体结构，结果表明Yb:CaYAlO4晶体属于四方晶系，空间群为I4/mmm。测试了Yb:CaYAlO4晶体的密度、热膨胀系数、比热、热扩散系数及热导率等物理性质，计算得到Yb:CaYAlO4晶体室温下沿a和c轴方向的热导率分别为3.6W/m/K和3.2W/m/K。测试了室温下Yb:CaYAlO4晶体的偏振吸收和发射光谱，通过F-L公式计算了Yb:CaYAlO4晶体的发射截面，得到在σ偏振下，Yb:CaYAlO4的发射光谱具有平滑且宽的特征，半高宽(FWHM)达到77nm，发射截面为0.8×10-20cm2，宽的发射谱有利于实现锁模超短脉冲激光输出。采用粉末浓度稀释法结合折射率匹配液来消除自吸收，测量了Yb3+在CaYAlO4基质中的荧光寿命为426μs。测试了室温下Yb:CaYAlO4晶体的上转换发光谱。首次实现了Yb:CaYAlO4晶体的连续和锁模激光输出，并获得了78fs的脉冲激光。研究表明，Yb:CaYAlO4晶体是有潜力的超短脉冲激光增益介质。 2. 采用提拉法生长了1at.% Nd:CaYAlO4晶体。通过ICP-AES方法测得Nd3+在CaYAlO4基质中的分凝系数为0.86。通过XRD粉末衍射法测定了Nd:CaYAlO4晶体结构，结果表明Nd:CaYAlO4晶体属于四方晶系，空间群为I4/mmm。测试了室温下Nd:CaYAlO4晶体的偏振吸收和发射光谱，并采用J-O理论计算了Nd:CaYAlO4晶体的光谱参数，室温下的偏振发射光谱表明Nd:CaYAlO4晶体对应于4F3/2→4I11/2跃迁的发射截面在π和σ偏振下分别为7.53×10-20cm2 (1068nm)和10.44×10-20cm2 (1080nm)，发射带宽(FWHM)分别为15nm和12nm，宽的发射带宽来自于基质晶格的无序性，使得发射谱非均匀展宽，有利于实现锁模脉冲激光输出。室温下Nd:CaYAlO4晶体的4F3/2能级的荧光寿命测试为129μs，经分析其量子效率接近于1。测试了Nd:CaYAlO4晶体的连续、调Q和锁模激光性能，实现了最大输出功率为5.16W的连续激光输出，对应斜效率为30.6%，激光波长为1080nm，此波长的激光可用来作为氦磁力计中氦原子的光学泵浦源；实现了Nd:CaYAlO4晶体的被动调Q激光输出，获得了脉冲宽度为10.6ns (a向晶体)和9.6ns (c向晶体)的稳定调Q激光输出；采用SESAM作为锁模器件，实现了Nd:CaYAlO4晶体的锁模激光输出，最大输出功率为2.25W，锁模脉冲宽度为3.9ps，表明Nd:CaYAlO4晶体是有潜力的超快皮秒激光器增益介质。 3. 采用提拉法生长了0.5at.%掺杂的Nd:Lu2SiO5 (Nd:LSO)，Nd:LuYSiO5 (Nd:LYSO)，Nd:GdYSiO5 (Nd:GYSO)，Nd:LuGdSiO5 (Nd:LGSO)晶体。采用ICP-AES方法测试了Nd3+在LSO、LYSO、GYSO和LGSO基质晶体中的分凝系数。采用XRD粉末衍射法测定了晶体结构，通过UnitCell软件计算了晶体的晶胞参数。测试了晶体的室温吸收和发射谱及荧光寿命谱，并通过J-O理论计算了其光谱参数，Nd:LSO、Nd:LYSO、Nd:GYSO和Nd:LGSO晶体对应于4F3/2→4I11/2跃迁的发射截面分别为6.6×10-20cm2 (1079nm)、7.84×10-20cm2 (1078nm)、3.8×10-20cm2 (1074nm)和4.39×10-20cm2 (1076nm)，发射带宽(FWHM)分别为5.1nm、6.1nm、8.8nm和9.8nm，宽的发射谱有利于实现锁模脉冲激光输出。实现了Nd:LSO、Nd:LYSO、Nd:GYSO和Nd:LGSO晶体的连续激光输出和Nd:LSO及Nd:LYSO晶体的被动锁模激光输出，在连续激光实验中，对于Nd:LSO、Nd:LYSO、Nd:GYSO和Nd:LGSO晶体获得的最大输出功率分别为2.54W、2.1W、1.54W和0.444 W，斜效率分别为29.6%、31.7%、27.4%和17.7%；在锁模激光实验中，对于Nd:LSO和Nd:LYSO晶体分别实现了12.3ps和8.9ps的锁模脉冲激光输出，最大功率分别为1.42W和1.7W，斜效率分别为16.7%和24.3%。研究结果表明，Nd:LYSO晶体由于拥有大的吸收和发射截面并且具有双波长锁模脉冲输出的特征，非常有潜力成为优异的皮秒脉冲激光器增益介质。 |
| 英文摘要 | Developing new diode pumped ultrafast lasers with high efficiency and high power has attracted more and more attentions in DPSSL. The disordered crystal matrices with Yb3+ or Nd3+ doping are considered to be the best choice for ultrafast laser medium. CaYAlO4 crystal belongs to tetragonal system, in which Ca2+ and Y3+ distribute randomly between AlO6 octahedral layers, besides, oxyorthosilicate crystals belong to monoclinic system, which can provide low symmetric and distorted crystal field for doped rare earth ions, and consequently the spectra of doped ions will be broadened. So both CaYAlO4 and oxyorthosilicate crystals are attractive as ultrafast crystal matrices. This thesis focuses on research about Yb3+/Nd3+ doped CaYAlO4 crystals and Nd3+ doped Lu2SiO5, LuYSiO5, GdYSiO5, and LuGdSiO5 crystals, including crystal growth by Cz method, crystal structure analysis, thermal property test, spectroscopic measurements, and laser performance studies. Main contents are as follows: 1. Yb:CaYAlO4 single crystal with excellent quality has been successfully grown by Cz method. The segregation coefficient of Yb3+ was measured to be 0.74 by ICP-AES, which demonstrated that Yb3+ can be easily doped into CaYAlO4 matrix. The crystal structure was analyzed by XRD. It shows Yb:CaYAlO4 crystal belongs to tetragonal system with space group of I4/mmm. The density, thermal expansion coefficient, specific heat, thermal diffusion coefficient, and thermal conductivity were measured. It is found that Yb:CaYAlO4 has thermal conductivity of 3.6W/m/K and 3.2W/m/K along a and c axis, respectively at room temperature. The polarized absorption and fluorescence spectra have been tested at room temperature. Through F-L formula, the emission cross section was calculated and it manifests that Yb:CaYAlO4 crystal has broad and smooth emission band at σ polarization, with FWHM up to 77nm and cross section of 0.8×10-20cm2. Broadband emission is favorable for generating ultrashort pulse lasers. Adopting powder concentration dilution method together with refractive-index-matched fluid to eliminate reabsorption effect, the fluorescence lifetime of Yb3+ was determined to be 426μs. The up conversion spectrum of Yb:CaYAlO4 crystal was recorded. The CW and mode-locked lasers have been realized on Yb:CaYAlO4 crystal for the first time, with pulse duration of 78fs. It indicates that Yb:CaYAlO4 crystal is a potential candidate as ultrafast laser medium. 2. 1at.% Nd:CaYAlO4 single crystal has been grown by Cz technique. The segregation coefficient of Nd3+ was determined to be 0.86 by ICP-AES. The crystal structure of as grown Nd:CaYAlO4 crystal was analyzed by XRD. It is shown that Nd:CaYAlO4 crystallized in tetragonal structure with space group of I4/mmm. The polarized absorption and fluorescence spectra have been measured at room temperature. The spectroscopic parameters were calculated by J-O theory. The emission cross sections have been determined to be 7.53×10-20cm2 at 1068nm and 10.44×10-20cm2 at 1080nm according to 4F3/2→4I11/2 transition at π and σ polarizations, respectively, with FWHM of 15nm and 12nm in turn. The broadband emission comes from disordered matrix structure, which is favorable for producing ultrashort pulse lasers. The room temperature fluorescence lifetime of 4F3/2 multiplet of Nd3+ was measured to be 129μs, resulting in a quantum efficiency near unity. The CW, Q-switched, and mode-locked laser performances were studied. The maximum output power of 5.16W was obtained in the CW regime, with corresponding slope efficiency of 30.6%, and laser wavelength was 1080nm, which can be used to pump helium in helium magnetometers. The pulse durations of 10.6ns and 9.6ns were obtained in passively Q-switched laser experiments on a and c orientation Nd:CaYAlO4 crystals, respectively. Employing SESAM as saturable absorber, 3.9ps mode-locked pulse laser was realized, with maximum output power of 2.25W. It demonstrates that Nd:CaYAlO4 crystal is a good candidate as ps ultrafast laser gain medium. 3. The 0.5at.% Nd3+ doped Lu2SiO5 (LSO), LuYSiO5 (LYSO), GdYSiO5 (GYSO), and LuGdSiO5 (LGSO) crystals have been grown by Cz method. The segregation coefficients of Nd3+ in LSO, LYSO, GYSO, and LGSO were measured. The crystal structures were analyzed by XRD and cell parameters were calculated using UnitCell software. The absorption and fluorescence spectra and fluorescence lifetime of these crystals were measured at room temperature. And spectroscopic parameters were calculated through J-O theory. The emission cross sections of Nd:LSO, Nd:LYSO, Nd:GYSO, and Nd:LGSO crystal at 4F3/2→4I11/2 transition were determined to be 6.6×10-20cm2 at 1079nm, 7.84×10-20 cm2 at 1078nm, 3.8×10-20cm2 at 1074nm, and 4.39×10-20cm2 at 1076nm, respectively, with FWHM of 5.1nm, 6.1nm, 8.8nm, and 9.8nm in turn. The broadband emission is favorable for producing ultrashort pulse lasers. The CW lasers of Nd:LSO, Nd:LYSO, Nd:GYSO, Nd:LGSO and mode-locked lasers of Nd:LSO, Nd:LYSO were realized. The maximum output power in CW regime of Nd:LSO, Nd:LYSO, Nd:GYSO, Nd:LGSO were obtained to be 2.54W, 2.1W, 1.54W, and 0.444W, respectively, with corresponding slope efficiency of 29.6%, 31.7%, 27.4%, and 17.7% in turn. In mode-locked laser experiments, the pulses with duration of 12.3ps and 8.9ps were obtained from Nd:LSO and Nd:LYSO crystal, respectively, with maximum output power of 1.42W and 1.7W, slope efficiency of 16.7% and 24.3%, respectively. It manifests that Nd:LYSO crystal has potential as ps ultrafast laser medium, due to its large absorption and emission cross section and dual wavelength laser output. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15710]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李东振. Yb/Nd掺杂超快激光晶体的生长及性能研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
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