利用计算全息技术重构激光超声的激发面源

把计算全息技术引入激光超声无损检测系统,此系统借助直接搜索算法生成计算全息图,利用空间光调制器液晶器件代替传统全息干板再现全息图像,并将此生成、再现方法具体用于空间调制的脉冲激光源的产生,以辅助固体表面的窄带超声波的激发。由于算法的稳健性和重建方法灵活性,大大简化了激光超声实验系统,缩短了实验周期,在激光超声无损检测领域有广泛的应用空间。     

Crystal growth,spectroscopic characteristics,and Judd–Ofelt analysis of Dy:Lu_2O_3 for yellow laser

Dy:Lu_2O_3 was grown by the float-zone(Fz) method. According to the absorption spectrum, the Judd–Ofelt(JO) parameters ?_2, ?_4, and ?_6 were calculated to be 4.86 × 10~(-20) cm~2, 2.02 × 10~(-20) cm~2, and 1.76 × 10~(-20) cm~2, respectively.The emission cross-section at 574 nm corresponding to the ~4F6_(9/2)→~6H_(13/2) transition was calculated to be 0.53 × 10~(-20) cm~2.The yellow(~4F_(9/2)→~6H_(13/2) transition) to blue(~4F_(9/2)→~6H_(15/2) transition) intensity ratio ranges up to 12.9. The fluorescence lifetime of the ~4F_(9/2) energy level was measured to be 112.1 μs. These results reveal that Dy:Lu_2O_3 is a promising material for use in yellow lasers.     

初中数学课堂教学中的有效对话

数学对话是人们就与数学相关的内容,以数学语言的形式发表意见、展示思考的过程,是相互理解、共同探究、传播数学文化的一种交际活动.课堂教学中的数学对话,主要包括三个方面:一是数学知识的对话,指学生以某种形式传递自己的数学思想和对知识的理解;二是数学体验的对话,指学生在学习过程中感受、情绪、认识、想法和意见的对话,实质是情感体验的对话;三是解决问题心得的对话.指学生选择恰当的描述和表达方式,呈现自己解决问题的思路、方法和结果的过程及反     

利用激光超声技术研究表面微裂纹缺陷材料的低通滤波效应

利用激光激发声表面波的理论模型,研究了被激发宽带声表面波在具有表面微裂纹缺陷金属材料上的传播特性.对具有不同形状的表面缺陷模型进行了数值分析.结果表明:表面微裂纹缺陷有明显的低通效应,缺陷深度越大高频截止频率就越低,缺陷深度与低通滤波的截止频率呈近似线性关系;缺陷的宽度增大对表面波透射能量有明显的衰减作用. 关键词： 激光超声 声表面波 有限元方法 低通滤波器     

冷坩埚法制备α-Al2O3多晶材料的工艺参数研究

采用冷坩埚法制备α-Al2O3多晶料,研究了引燃剂的形态、坩埚下降的速率、加料速率等工艺参数变化对所成形晶碇质量的影响。结果表明:采用的引燃剂为高纯铝片,坩埚下降速率为10 mm/h,采取加料速率为1 kg/min的最佳工艺条件,可制备出高致密度、高纯度的α-Al2O3多晶料。采用排水法测密度,用电感耦合等离子体原子发射光谱仪(ICP-OES)对原料粉和多晶块料中Ca、Fe、Na、Mg、K、Ti、Si、Cr等元素进行测定。结果表明:多晶块料中白色可用部分Ca、Fe、Na、K、Ti、Si、Cr等元素明显降低,说明采用冷坩埚法制备的氧化铝多晶料对原料粉具有一定的提纯作用,并且测量其堆积密度为2.6～2.8 g/cm3。因此采用冷坩埚法制备的α-Al2O3多晶料符合目前生长大尺寸蓝宝石对原料的要求。     

Spectroscopic properties of Er/Ce-codoped La3Ga5SiO14

The Er-single-doped and Er/Ce-codoped La₃Ga₅SiO₁₄ polycrystalline powders are synthesized by the solid-phase synthesis method. The room-temperature luminescence spectra of the samples are investigated. The Near-infrared-region spectroscopic properties of Er³⁺ ions in the La₃Ga₅SiO₁₄ systems are analysed with Judd-Ofelt theory and rate equations. The effective deactivating effect of Ce³⁺ ions on Er³⁺ ions is confirmed.     

Growth and spectroscopic characteristics of Nd-doped PbWO₄ crystal

Nd-doped PbWO4 crystals are grown by using the modified Bridgman method.The spectroscopic properties of the crystals are investigated.The changes of the absorption band at 350 nm are discussed for samples annealed at 740℃ and 1040℃.The radiative lifetime of the 4 F 3/2 level is calculated by using the Judd-Ofelt theory according to the absorption spectrum of 0.5 at.% Nd-doped PbWO 4 crystal.The spontaneous Raman scattering properties of the crystals are analysed.     

Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method

Transient thermal grating method is used to measure the thermal diffusivity of absorbing films deposited on transparent substrates. According to periodically modulated dielectric constant variations and thermoelastic deformations of the thin films caused by the transient thermal gratings, an improved optical diffraction theory is presented. In the experiment, the probing laser beam reflectively diffracted by the thermal grating is measured by a photomultiplier at different grating fringe spaces. The thermal diffusivity of the film can be evaluated by fitting the theoretical calculations of diffraction signals to the experimental measured data. The validity of the method is tested by measuring the thermal diffusivities of absorbing ZnO films deposited on glass substrates.     

Yb:CaYAlO4再生放大器

阿秒科学是驱动超强超快激光往高平均功率和短脉冲宽度方向快速发展的动力之一.本文针对高重复频率阿秒光源的实际需求,开展了基于国产Yb:CaYAlO₄晶体的再生放大理论和实验研究.在理论研究中,根据Yb:CaYAlO₄晶体的热透镜计算结果,设计了热稳定性良好的模式可调再生腔;并对晶体π和σ偏振的放大输出能量和光谱进行计算.在此基础上,开展了Yb:CaYAlO₄晶体不同偏振性质的再生放大实验研究.在晶体π偏振的实验中,获得了平均功率16.1 W、单脉冲能量1.61 mJ、光谱中心波长1030 nm、光谱半高全宽16 nm的放大输出,压缩后的激光脉冲宽度为149 fs,压缩效率为92.1%,峰值功率大于9.5 GW.在σ偏振获得了平均功率28.7 W、单脉冲能量2.87 mJ、光谱中心波长1037 nm、光谱半高全宽11 nm的放大输出,压缩后的激光脉冲宽度为178 fs,压缩效率为91.5%,峰值功率大于14.2 GW,光束质量因子M² <1.2.以上研究结果实现了目前Yb:CaYAlO_4...     

固体中脉冲激光激发声表面波的理论研究

本文运用本征函数展开的方法对固体材料中脉冲激光激发的声表面波进行了理论研究，在考虑热弹激发的条件下，利用三维的轴对称模型，得到了脉冲激光光源的脉冲宽度以及聚焦半径对固体材料中声表面波信号的时域及频域的影响，对进行超短脉冲激光激发超声的研究具有指导意义。