Nd:YAG透明陶瓷制备技术的研究进展

掺钕钇铝石榴石(Nd：YAG)透明陶瓷是新一代固体激光材料。同Nd：YAG单晶和钕玻璃相比，Nd：YAG透明陶瓷及其制备技术具有许多优点，例如可获得掺杂浓度更高、尺寸更大的材料，可实现多层、多功能陶瓷复合结构，同时成本较单晶生长低，可实现大规模生产等，因而受到广泛重视。文中对近年来Nd：YAG透明陶瓷激光材料的研究进展、制备技术及其激光器的发展进行了综合评述，并展望了其应用前景。     

固相反应法制备高浓度掺杂Nd:YAG激光透明陶瓷及其性能

用固相反应和真空烧结技术,成功制备了高质量的4.0%(摩尔分数)Nd:YAG透明陶瓷,并对样品的显微结构、光学透过率、光谱性能和激光性能进行了表征.结果表明:样品的平均晶粒尺寸约为10 μm;样品(厚度为2.8 mm)在1 064 nm处的透过率高达79.5%;主吸收峰位于807 nm处,峰值吸收系数为13.9 cm-1,激光波长1 064 nm处的吸收系数为0.2 cm-1;主荧光发射峰位于1 064 nm处,荧光寿命为102 μs.用激光二极管(808 nm)端面泵浦Nd:YAG陶瓷样品(泵浦源最大输出功率为1 000 mW),获得了波长为1 064 nm的连续激光输出,输出功率17 mW(最大泵浦吸收功率为998 mW),斜率效率为6.1%,激光阈值约733 mW.     

Nd:YAG透明陶瓷的制备及激光输出

用溶胶-凝胶法制备了Nd3+掺杂摩尔分数为2.7%的Nd:AG粉体。采用真空热压和热等静压相结合工艺制备了Nd:YAG透明陶瓷。测试了样品的显微结构、透过光谱、吸收光谱、荧光光谱和激光性能。结果表明:样品的晶粒尺寸为2～10μm,晶界处存在少量气孔;1.7mm厚样品1064nm波长的透过率为78%;样品808nm处吸收峰对应的吸收系数为27.5cm-1;808nm泵浦的主荧光峰位于1064nm,荧光寿命为135μs;LD端面泵浦尺寸3mm×3mm×1.5mm的样品获得了最大输出功率170mW的激光输出,光-光转换效率为8%,斜效率为13.8%。     

钕镱共掺钇铝石榴石纳米粉体

采用溶胶-凝胶燃烧法,制备了钕镱共掺钇铝石榴石(Nd3+/Yb3+:YAG)透明陶瓷纳米粉体,并用热分析、X射线衍射、红外光谱、透射电镜、吸收及荧光光谱等测试方法对其结构、形貌及性能进行分析.结果表明:经900℃煅烧,Nd3+/YB3+:YAG透明陶瓷的质量损失为49.56%,所得到的Nd3+:Yb3+:YAG纳米粉体结晶好,烧结性好,纯度较高,形状规则,粒径均匀,均在60～100衄之间.在808 nm处具有较强的吸收带,对应于Nd离子4I9/2-4F7/2跃迁,有利于对808nm激光二级管泵浦光的吸收.在1064nm处,Nd3+/Yb3+:YAG的发射峰要强于Nd3+:YAG,说明在Nd3+/Yb3+:YAG中,通过[(4F3/2)Nd),(2F7/2)Yb]→[(4I9/2)nd,(2F5/2)Yb]离子问的交叉弛豫,产生了有效的Yb3+到Nd3+的能量转移,从而实现激光的高效输出.     

钛宝石激光器泵浦(Cr4+,Nd3+):YAG晶体的自调Q激光器

用钛宝石激光器泵浦单块(Cr4+, Nd3+:YAG)晶体获得了1.064 μm的自调 Q激光输出.激光输出的模式是稳定的单纵模, 泵浦的阈值功率为63 mW, 脉冲宽度(F WHM)为8 ns, 斜率效率高达24%.随着泵浦功率的变化, 脉冲宽度保持不变, 而重复频率则在变化.这种把激光增益介质和可饱和吸收体结合到一起的自调Q激光晶体的研究将有利于固体激光器的全固化、集成化和实用化.     

钛宝石激光器泵浦(Cr~(4 ),Nd~(3 ))∶YAG晶体的自调Q激光器

用钛宝石激光器泵浦单块 (Cr4 ,Nd3 ∶YAG)晶体获得了1.0 6 4μm的自调Q激光输出 .激光输出的模式是稳定的单纵模 ,泵浦的阈值功率为 6 3mW ,脉冲宽度 (FWHM)为 8ns,斜率效率高达2 4% .随着泵浦功率的变化 ,脉冲宽度保持不变 ,而重复频率则在变化 .这种把激光增益介质和可饱和吸收体结合到一起的自调Q激光晶体的研究将有利于固体激光器的全固化、集成化和实用化 .     

高掺杂浓度Yb:YAG晶体的生长及激光性能

用引上法生长了30％Yb:YAG(摩尔分数,下同）晶体,研究了晶体的生长工艺参数和退火工艺参数;用940nm吸收系数表征了Yb^3 离子在Yb:YAG晶体中的分布情况,结果表明：Yb^3 离子在Yb:YAG晶体中分布均匀,研究了晶体微片的激光特性,用钛定石激光器泵浦30％Yb:YAG微片,获得了1．053μm的高效激光输出。     

埋粉热压后处理制备Nd∶YAG激光陶瓷

以市售高纯氧化物粉体为原料,采用固相反应烧结—埋粉热压后处理组合烧结工艺制备了直径为30mm、厚度为3.05mm的Nd3+∶Y3Al5O12(Nd∶YAG)透明陶瓷样品。研究了埋粉热压后处理工艺对Nd∶YAG陶瓷的光学性能、残留应力和光学均匀性等的影响。研究表明,通过将真空烧结后的Nd∶YAG陶瓷埋入BN粉体中进行热压后处理,克服了Nd∶YAG陶瓷在热压过程中容易碎裂及碳污染问题,并进一步排除了Nd∶YAG陶瓷内部的残留气孔,其透过率大于80%。埋粉热压后处理工艺对Nd∶YAG陶瓷的残留应力分布和光学均匀性没有影响。采用光纤耦合808nm激光二极管泵浦Nd∶YAG陶瓷样品,实现了连续瓦级激光输出,最高输出功率为3.6W,光光转换效率为20%。     

掺Yb3+的氧化镧钇透明激光陶瓷的光谱特性

采用传统陶瓷烧结工艺,在无压还原气氛中低温制备了Yb3 掺杂量高达10%(按摩尔计)的透明性良好的氧化镧钇激光陶瓷,研究了其在室温的吸收光谱、发射光谱以及荧光寿命.结果表明:掺Yb3 氧化镧钇透明激光陶瓷具有宽的吸收和发射光谱以及长的荧光寿命.吸收峰位于902,942nm和968nm处,吸收截面分别为0.31×10-20,0.45×10-20cm2和0.53×10-20cm2;主发射峰位于1 032nm和1 075 nm处,发射截面分别为1.05×10-20cm2和0.87×10-20 cm2,上能级荧光寿命分别为1.17ms和1.04ms.掺Yb3 氧化镧钇透明激光陶瓷大的吸收和发射截面以及长的荧光寿命有利于高效吸收泵浦能量,是一种适合于高效、高功率激光二极管泵浦的固体激光介质.     

Nd:YSAG透明陶瓷的制备及激光实验

以氧化钇(99.99%,质量分数,下同)、氧化钕(99.99%)、硝酸铝(分析纯)、乙二胺四乙酸(C10H16N2O8,分析纯,EDTA)为原料,经过成型、素烧最终在氢气气氛中用燃烧法制备了掺钕的钇铝钪石榴石[Ndx:Y3(1-x)(Scy,Al2-y)Al3O12,Nd: YSAG]粉体.结果表明:采用这种方法在900℃可以合成Nd: YSAG单相粉体,在氢气气氛中1850℃烧结6h可以获得较好的Nd: YSAG粉体,即制备的Nd: YSAG粉体具有很好的烧结活性.在Nd: YSAG透明陶瓷中,Nd的摩尔分数可达6%,甚至更高,样品的透过率依然很好.Nd: YSAG透明陶瓷具有谱线较宽的特点.实验中,用激光Ti: sapphire作为泵浦源,采用平凹腔结构获得了激光输出为10mW.     

钇铝石榴石(YAG)激光透明陶瓷研究进展

钇铝石榴石(YAG)激光透明陶瓷由于具有单晶、玻璃激光材料无可比拟的优势而成为研究热点,并得到迅速发展,高性能的稀土元素掺杂YAG透明激光陶瓷被相继报导.本文综述了近年来国内外关于YAG激光透明陶瓷的最新研究成果.主要包括YAG微细粉体合成、烧结添加刺及多晶YAG透明陶瓷的致密化烧结技术,并对比了YAG透明陶瓷相对于Y...     

Multilayer YAG/Re:YAG/YAG laser ceramic prepared by tape casting and vacuum sintering method

This paper reports the use of tape casting and vacuum sintering process for the fabrication of optical grade YAG/Re:YAG/YAG (Re = Yb or Nd) composite laser ceramic. The influence of dispersant content on the rheological behavior of the slurry, the microstructure, the optical and laser performances, were studied. The experimental results showed that laser output at 1030 nm was generated for YAG/Yb:YAG/YAG with threshold absorbed pump power of 4.33 W and slope efficiency of about 12% when the transmission of output coupler (T_oc) was 2.3%. For YAG/Nd:YAG/YAG ceramic, 1064 nm laser output was obtained, and the slope efficiency increased from 30% to 38% while T_oc changed from 2.3% to 10%.     

Synthesis and Performance of Advanced Ceramic Lasers

This paper reports recent progress in the production of polycrystalline Nd:YAG (Y₃Al₅O₁₂), Nd:YSAG (Y₃Sc_1.0Al_4.0O₁₂), Yb:YSAG ceramics, and a Nd-doped YAG single crystal with an almost perfect pore-free structure by advanced ceramic processing. The laser conversion efficiency of pore-free polycrystalline Nd- and Yb-doped ceramics is extremely high, and their optical qualities are comparable with that of commercial high-quality Nd:YAG single crystals. We have also succeeded in the fabrication of a Nd:YAG single crystal, which can be used for laser oscillation, by the solid-state reaction method. Laser oscillation efficiency was very low when the pores remained inside the single crystal; however, the laser oscillation efficiency of the pore-free Nd:YAG single crystal was slightly higher than that of polycrystalline Nd:YAG ceramics having high optical quality. From this fact, it was recognized that optical scattering occurs mainly in the residual pores inside the Nd:YAG ceramics and the scattering at the grain boundary is very less. In addition, we confirmed that a heavily doped Nd:YAG single crystal can be fabricated by the sintering method. Moreover, we have demonstrated the fabrication of a composite ceramic with complicated structures without the need for precise polishing and diffusion bonding. Advanced ceramic processing, which enables design flexibility of the laser element, presented in this work is important in the development of a high-performance laser (high efficiency, high beam quality, and high output energy, etc.)     

Effects of Neodymium Concentration on Optical Characteristics of Polycrystalline Nd:YAG Laser Materials

A neodymium-doped yttrium-aluminum garnet (Y₃A1₅O₁₂, YAG) (Nd:YAG) ceramic that contained 0.3–4.8 at.% neodymium additives and exhibited nearly the same optical properties as those of a single crystal was fabricated by a solid-state reaction method using high-purity powders. Although the integrated absorption intensity of the ²H_9/2+⁴F_5/2 bands simply increased as the neodymium concentration in the YAG ceramics decreased, the fluorescence intensity of the 2.4 at.% Nd:YAG ceramic was the strongest among Nd:YAG ceramics with various neodymium concentrations and a 0.9 at.% Nd:YAG single crystal. An oscillation experiment was performed on a continuous-wave (cw) laser with a diode-laser exciting system using those ceramics and the single crystal. The oscillation threshold and slope efficiency in that analysis were 309 mW and 28%, respectively, for the 1.1 at.% Nd:YAG ceramics and 356 mW and 40%, respectively, for the 2.4 at.% Nd:YAG ceramics. The lasing characteristics of the ceramics in the present work were superior to those of a 0.9 at.% Nd:YAG single crystal that was fabricated by the Czochralski (Cz) method.     

Preparation of a Φ60 mm Nd:YAG transparent ceramic disk

A high quality Nd:YAG transparent ceramic disk (Φ60 mm×2 mm) has been prepared by the solid-state reactive sintering technique, which was sintered satisfactorily at 1780 °C for 20 h. The high transparency of the sample has been assured by its pore-free microstructure and pure YAG phase composition with the in-line transmittances up to 84.5% at 1064 nm and 82.5% at 400 nm, respectively. The optical homogeneity of the disk was evaluated by the interference stripes with the PV and RMS values being 0.099 λ and 0.013 λ, respectively. The maximum output power of 2052 W with the slope efficiency of 39.0% was obtained at 500 Hz repetition rate. Results indicated that the Nd:YAG transparent ceramics could be a potential option for high power disk laser.     

激光二极管泵浦Nd:NaY(WO4)2晶体的激光性能

采用提拉法生长了平均尺寸为φ25 mm×50 mm的掺钕钨酸钇钠[Nd:NaY(WO4)2,Nd:NYW]晶体,测量了Nd:NYW晶体的吸收光谱.吸收光谱表明:该晶体在804,752 nm和586 nm附近的吸收峰较强、较宽,有利于用激光二极管(laser diode,LD)泵浦.分别以氙灯和LD作为泵浦源,对晶体的激光特性进行了研究.结果表明:当氙灯输入能量为11.7 J时,该激光棒获得了36.9 mJ的输出;当LD泵浦功率为1 w时,输出273 mW的1.06 μm波长激光,激光阈值为160 mW,光-光转换效率为27.3%,斜效率为34%.     

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

Large and nondeforming Nd: YAG ceramic prepared by wet forming is of great importance as gain medium to obtain high-power solid-state lasers. However, it is difficult to achieve high-quality laser ceramics due to insufficiency of the in-depth understanding of transformation mechanism of gels viscoelasticity and effective control means during drying process. In this work, the rheological behaviors, viscoelastic characteristics, and mechanical strengths in classical acrylamide (AM) and novel Isobam (PIBM) gelcastings were systematically compared to explore the suitable route for the large-sized 2% Nd: YAG transparent ceramics with high aspect ratio (>10). AM system exhibited a higher complex viscosity (1.82 × 10⁵ Pa s), a shorter gel time (92.9 seconds), and a higher flexural strength (about 24.46 MPa) than PIBM system, and especially its ability to quickly gel was beneficial to the homogeneity of green body. In addition, the order of drying rates of wet gels in four drying media was observed as follows: 55℃ hot air> ethanol> solid desiccant> PEG-11000 and the moisture diffusion coefficients were calculated and simulated to offer the deep consideration of drying kinetics. The “ethanol + 55℃ hot air” was regarded as an effective composite drying method to eliminate defect and to achieve φ8 mm × 160 mm Nd: YAG ceramic with the in-line transmittance of 83% @1064 nm. Therefore, not only the cognition of gel process, but also the defects control strategy is proposed. More importantly, this work greatly promotes the application of wet forming and laser ceramics in high-power lasers.     

Surface and Mirror Twin Grain Boundary Segregation in Nd:YAG: An Atomistic Simulation Study

Ceramic lasers have advantages such as better optical homogeneity, cheaper production, and more freedom in shape compared with monocrystalline lasers. However, equal or better laser performances are required. Interface segregation is important as ceramics contain a high number of interfaces, segregation to which may locally alter the concentration of luminescent dopants, which in turn may influence laser performance. The present work applies atomistic simulation techniques to investigate the segregation of neodymium (Nd) dopants to surfaces and mirror twin grain boundaries in yttrium aluminum garnet (YAG). These results allow a better understanding of interfacial segregation and its influence on laser performance of Nd:YAG ceramics.     

A novel route to fabricate Yb:YAG ceramic fiber and its optical performance

Transparent laser ceramics are the attractive gain medium for solid-state lasers. However, they have not been applied to the fiber lasers due to the difficulty of forming green fibers by traditional methods. In this study, a novel route combined aqueous gelcasting with capillary glass tube was designed to prepare Yb:YAG transparent ceramic fiber with a diameter of 1.0 mm and 43.0 mm in length for the first time. The slurry with high solid loading and low viscosity was smartly inhaled into the capillary glass tube to conquer the difficulty of casting. The green fibers without cracks and deformation had highly dense microstructure. The in-line transmittance of highly doped 15.0 at.% Yb:YAG transparent ceramic disc prepared from the same preparation conditions of Yb:YAG ceramic fiber was 80.0 % at 1064 nm. This study provides a novel route to prepare transparent ceramic fiber differing from extrusion processing, promoting the development of fiber laser.