蓝宝石基片上制备大面积Tl2Ba2CaCu2O8超导薄膜

在2英寸双面蓝宝石基片上采用CeO₂作为缓冲层制备了高质量Tl₂Ba₂CaCu₂O₈(Tl-2212)超导薄膜.以金属铈作为溅射靶材,采用射频磁控反应溅射法生长了c轴织构的CeO₂缓冲薄膜,并研究了不同生长条件对于CeO₂缓冲层的晶体结构及表面形貌的影响.超导薄膜采用直流磁控溅射和后热处理的方法制备.扫描电子显微镜(SEM)图像显示,超     

加热功率波动对SAPMAC法生长蓝宝石晶体的影响

本文根据温度波在熔体介质中的传播理论,结合SAPMAC法蓝宝石晶体生长工艺特点,研究了由加热功率波动引起的温度波动对晶体生长的影响.研究表明由于氧化铝高温熔体具有较大的热扩散系数,温度波较容易传到固液界面引起界面温度起伏;界面的温度起伏会使晶体内产生气泡、空腔等缺陷.根据温度波的频率、幅值对氧化铝熔体的传递深度、衰减规律的关系,提出了提高系统热惯性、增加界面熔体包裹层厚度等抑制措施.     

Experimental study on injection-locked Ti:sapphire lasers

An injection-locked Ti:sapphire laser is developed,with injection locking achieved using the Pound-DreverHall technique.By measuring the dependence of output power on the pump power with various Ti:sapphire laser parameters,we experimentally studied the influences of the ring cavity length,the focal length of the pump-laser mode-matching lens,and the output-coupler transmission on the threshold and slope efficiency.The dependence of the output power on the master laser power is also investigated.The present study provides a guideline for developing a Ti:sapphire laser with high slope efficiency and low threshold.     

Occurrence and elimination of in-plane misoriented crystals in AIN epUayers on sapphire via pre-treatment control

AlN epilayers are grown directly on sapphire （0001） substrates each of which has a low temperature AlN nucleation layer. The effects of pretreatments of sapphire snbstrates, including exposures to NH3/H2 and to H2 only ambients at different temperatures, before the growth of AlN epilayers is investigated. In-plane misoriented crystals occur in N-polar AlN epilayers each with pretreatment in a H2 only ambient, and are characterized by six 60°-apart peaks with splits in each peak in （1012） phi scan and two sets of hexagonal diffraction patterns taken along the [0001] zone axis in electron diffraction. These misoriented crystals can be eliminated in AlN epilayers by the pretreatment of sapphire substrates in the NH3/H2 ambient. AlN epilayers by the pretreatment of sapphire substrates in the NH3/H2 ambient are Al-polar. Our results show the pretreatments and the nucleation layers are responsible for the polarities of the AlN epilayers. We ascribe these results to the different strain relaxation mechanisms induced by the lattice mismatch of AlN and sapphire.     

不同基质掺Yb~(3+)光纤的单频极限输出功率

综合分析了不同基质掺Yb3+光纤的材料特性,在改进的极限输出功率理论模型的基础上,对Yb3+掺杂的硅光纤、磷酸盐光纤、YAG晶体(或陶瓷)光纤以及蓝宝石光纤的单频极限输出功率特性进行了详细分析。计算结果表明,YAG晶体(或陶瓷)光纤和蓝宝石光纤单频极限输出功率可以达到10kW以上。分析了单模情况下的极限输出功率,结果表明YAG晶体(或陶瓷)光纤和蓝宝石光纤在单模情况下也有较大优势,目前的单频激光功率还有很大的提升空间。对于单频激光光纤材料而言,降低受激布里渊散射(SBS)增益系数、提高导热性能是提高极限输出功率的有效途径。     

基于小波变换的蓝宝石荧光光纤温度计

采用激光加热小基座法生长出掺Cr3+的蓝宝石光纤荧光温度传感头，它具有结构紧凑，耐高温等特点，测温范围从室温到450℃。使用基于小波变换的数据处理方法，有效去除信号中的噪声，提高了信噪比。在对荧光测温机理和有关光纤技术进行分析的基础上，采用与调制荧光信号相关的双参考源相位锁定测量方案，可在无激励光干扰的情况下对荧光寿命进行实时测量。根据噪音和信号在小波变换下表现出的不同性质，提出以小波变换为基础的温度信号特征提取及消噪方法。与其它处理方法相比，小波变换方法可以克服傅里叶变换对突变信号不起作用的缺点，同时又比Gabor变换具有可变窗口的优点。该方法可以缩短测量时间，提高测量分辨率。     

激光超声技术测量高温下蓝宝石单晶的弹性模量

利用纳秒激光脉冲所激发的超声纵波, 非接触地测量了蓝宝石单晶沿c轴方向的弹性模量 C₃₃随温度的变化关系. 结果表明, 在室温到1000 ℃ 的范围内, 蓝宝石的弹性模量C₃₃随温度T的升高而减小, 两者之间近似呈如下二次关系: C₃₃ = - 1.541× 10^-5T² - 0.021T + 498.3. 由于该方法利用激光烧蚀效应激发出了强度很大的纵波, 因此对弹性模量的测量具有较高的精度, 估算C₃₃的测量误差不超过0.1%.     

Stress and morphology of a nonpolar a-plane GaN layer on r-plane sapphire substrate

The anisotropic strain of a nonpolar (1120) a-plane GaN epilayer on an r-plane (1102) sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.     

低阈值掺钛蓝宝石激光器实验研究

结合特殊的谐振腔设计和半导体可饱和吸收镜，建成了一台低阈值的自启动掺钛宝石激光器 . 分别用3％和12％的输出耦合镜，获得了阈值低至390mW和600mW的稳定锁模脉冲输出. 采 用12％输出耦合镜，在12W抽运时，输出平均功率为114mW，对应的典型脉宽为17fs，谱宽 为47nm. 相对于以往的低阈值克尔透镜锁模激光器，锁模工作的范围区域加宽，减小了操作 难度，提高了稳定性. 关键词： 低阈值 半导体可饱和吸收镜 克尔透镜锁模 掺钛蓝宝石激光器