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1.
分别在室温(25℃)和高温(300℃)下,通过X射线衍射实验对MgF2和SrF2晶体进行了晶体结构的检测.利用基于Rietveld精修方法的RIETAN-2000程序对所得实验结果进行了解析,精修了MgF2和SrF2晶体在不同温度下的各晶体结构参数,获得了原子各向同性温度因子B.通过Maximum Entropy Meth-od ( MEM)解析得到了MgF2和SrF2晶体的等高电子密度分布图谱,实现了电子密度分布的可视化.  相似文献   

2.
为了确定ZrO2和(ZrO2)0.97(Bi2O3)0.03的晶体结构和原子热振动各向同性温度因子B,对该粉末晶体进行X射线衍射实验,建立了晶体结构模型,进行晶体结构分析。首先,采用共沉淀法和高温固相烧结法制备了纳米氧化锆ZrO2和(ZrO2)0.97(Bi2O3)0.03粉末晶体,接着,使用X射线测试仪对两种样品进行了衍射实验(XRD),利用Rietveld 精修方法的 RIETAN-2000程序对所得实验结果进行了晶体结构分析,获得了晶体结构参量和原子热振动各向同性温度因子B。通过Maximum Entropy Method(MEM)解析得到了粉末晶体(ZrO2)x(Bi2O3)1-x(x=1.0,0.97)的等高电子密度分布可视化图谱。结果表明,(ZrO2)0.97(Bi2O3)0.03的晶胞体积比ZrO2的晶胞体积大分别为140.6850 Å3和140.5637Å3;ZrO2晶体的原子热振动各向同性温度因子B(Zr)、BO(1)、BO(2)和 B(Bi)分别为0.690、0.269、 0.178 和 0 Å2,(ZrO2)0.97(Bi2O3)0.03晶体的分别为0.460 、0.583 、0.121 和0.581 Å2。 确定了(ZrO2)0.97(Bi2O3)0.03的晶体结构属于单斜晶系,实现了等高电子密度分布三维(3D)和二维(2D)的可视化,进一步确定了晶体结构和原子位置。  相似文献   

3.
利用GN-2型高能球磨机研磨了Y_2O_3粉末晶体,用BT-1600图像颗粒分析仪对研磨时间为0h和20h的两份样品进行了分析.室温条件下,利用X射线衍射实验检测了晶体结构的变化,并且利用RIETAN-2000程序进行了晶体结构精修得到了原子热振动的大小.运用MEM解析方法实现了2D(平面)和3D(立体)的等高电子密度分布的可视化.  相似文献   

4.
岳廷  何灏  张星  李广 《物理学报》2011,60(5):57501-057501
运用X射线衍射(XRD)分析技术,对钙钛矿型La0.55Ca0.45MnO3化合物的空间结构进行了变温测量,用Rietveld方法对XRD实验数据进行了精修拟合.随着温度的降低,实验上观测到衍射峰的劈裂,暗示该化合物内部晶体结构发生了相变.磁化曲线测量表明,对应晶体结构相变的温度,化合物的磁性也发生由铁磁性向反铁磁性的转变.运用Rietica软件对化合物的XRD数据进行了处理,得到了La0.55Ca0.45< 关键词: 锰氧化物 相变 电子密度分布 磁结构  相似文献   

5.
利用传输矩阵方法对一维Ag/MgF2光子晶体的带隙特性进行了研究。构建了由Ag和MgF2组成的一维光子晶体结构模型,以此模型为基础详细讨论了填充比、周期层数、入射角等参数对光子晶体带隙结构的影响,并讨论了造成吸收的原因。研究结果表明,与其他金属光子晶体的研究结果相比,该结构的金属光子晶体在紫外线波段具有高反射率的光子带隙,属于不完全带隙的一维光子晶体,适用于制作紫外线波段的光学反射镜。  相似文献   

6.
Co掺杂MgF2电子结构和光学特性的第一性原理研究   总被引:2,自引:0,他引:2       下载免费PDF全文
基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了Co掺杂MgF2晶体的几何结构、电子结构和光学性质.结果表明,Co掺杂导致MgF2晶体结构畸变,可能发生一种类四方和斜方型结构相变.由于Co原子的加入,体系的禁带宽度减小,可观察到半导体-金属性转变.计算也表明,Co掺杂对静态介电常数和光吸收系数有重要调制作用,所得结果与最近实验测量很好相符,揭示了Co:MgF2体系在光学元器件方面的潜在应用.  相似文献   

7.
热退火对KDP晶体损伤阈值的影响(英)   总被引:1,自引:1,他引:0       下载免费PDF全文
研究了不同退火温度下磷酸二氢钾(KDP)晶体的透过光谱和损伤阈值的变化。发现热退火对晶体的透过光谱没有影响,退火温度分别为140 ℃和160 ℃时晶体的损伤阈值没有明显变化。但是在150 ℃下,晶体的损伤阈值提高了约1.4倍。实验证明150 ℃下的热退火对提高晶体的损伤阈值效果最好。  相似文献   

8.
利用X射线衍射(XRD)、角分辨光电子能谱(ARPES)和能带计算的方法研究了不同温度下γ-PtBi2的晶体结构。利用单晶XRD确定了室温下晶体的结构为P31m。为了确定低温时样品的晶体结构,用ARPES测得了样品的电子结构并与计算结果进行了对比,结果显示样品的结构与P31m相吻合,这表明在低温时样品依然保持P31m结构。进一步的高温XRD研究表明,在高温时样品的晶体结构仍为P31m结构。  相似文献   

9.
在激光等离子体相互作用过程中,受激拉曼散射(SRS)会通过Langmuir波衰减不稳定性(LDI)和电子俘获两种机理饱和.文章给出均匀一维等离子体和低强度非相对论激光作用中,LDI和电子俘获两种机理下的SRS饱和时间的解析表达式.SRS饱和时间与入射激光强度,电子密度,电子温度,初始电子密度微扰等参数有关.解析理论计算得到了与模拟和实验相符的结果. 关键词: 受激拉曼散射 饱和 Langmuir波衰变不稳定性(LDI) 电子俘获  相似文献   

10.
在室温条件下的激光晶体MgF2单晶中,实验发现含有130多条峰的电子自旋共振(ESR)波谱。两个样品分别取自MgF2单晶生长放肩的尖锥部位和MgF2:Co晶体.两个样品都没有经过任何辐照处理。两个样品具有相同的各向异性谱,说明掺入的Co2+离子引发了与MgF2单晶放肩部位相同的位错缺陷,产生了相同的多核固体自由基。这些顺磁固体自由基稳定且寿命长,产生的ESR信号是各向异性的。经初步计算拟合,谱线是由三种不同的多核自由基产生的。当磁场方向与晶体的[100]或[010]方向平行时,样品的ESR信号出现在磁场从0.2292特斯拉(T)到0.4654T的0.2362T范围内(相当于能带宽度为0.233eV)。最窄的线宽DH约为0.00128特斯拉,DH相当于相邻的能级差,是非常小的,仅有1.85×10-7eV 或1.46×10-3cm-1。这一事实表明其基态简并度是相当高的,在不太高的直流磁场下几乎是一个由准连续的能级组成的能带。这有可能成为可调谐的固体激光介质的新基点。  相似文献   

11.
Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.  相似文献   

12.
A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.  相似文献   

13.
The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.  相似文献   

14.
15.
Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·104 Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.  相似文献   

16.
A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.  相似文献   

17.
A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly.  相似文献   

18.
We experimentally demonstrate amplitude squeezed soliton utilizing intensity-dependent self-phase modulation in an asymmetric Sagnac interferometer.The system.whose components are connected via ferrule connector/physical connection(FC/PC)fiber connectors,constitutes all-fiber configuration to generate squeezed soliton.Soliton amplitude reduction measured by homodyne detection is near 4.0 dB below the shot-noise level.Optimal squeezing fields in both simple and compact all-fiber configuration are obtained.  相似文献   

19.
The(2 1)-dimensional nonlinear Schr(o)dinger(NLS)equation with spatially inhomogeneous nonlinearities is investigated,which describes propagation of light in(2 1)-dimensional nonlinear optical media with inhomogeneous nonlinearities.New types of optical modes and nonlinear effects in optical media are presented numerically.The results reveal that the regular split of beam can be obtained in (2 1)-dimensional nonlinear optical media with inhomogeneous nonlinearities,by adjusting the guiding parameter.Furthermore,the stability of beam regular split is discussed numerically,and the results reveal that the beam regular split is stable to the finite initial perturbations.  相似文献   

20.
In the real-world application of face recognition system, owing to the difficulties of collecting samples or storage space of systems, only one sample image per person is stored in the system, which is so-called one sample per person problem. Moreover, pose and illumination have impact on recognition performance. We propose a novel pose and illumination robust algorithm for face recognition with a single training image per person to solve the above limitations. Experimental results show that the proposed algorithm is an efficient and practical approach for face recognition.  相似文献   

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