Fe、Ni共掺杂ZnO基稀磁半导体光学性能与铁磁性研究

采用水热法成功制备了不同掺杂浓度的Zn1-2x Fe x Ni x O(x=0,0.025,0.05,0.1)稀磁半导体材料,利用X射线衍射(XRD)、透射电子显微镜(TEM)和X射线能量色散分析仪(XEDS)对样品进行表征,并结合拉曼(Raman)光谱、光致发光光谱(PL)和振动样品磁强计(VSM)研究样品的光学性能和磁学性能。结果表明,水热法制备的样品具有结晶性良好的纤锌矿结构,没有杂峰出现,形貌为纳米棒状结构,分散性良好。Fe2+、Ni2+是以替代的形式进入ZnO晶格中,Fe和Ni的掺杂使得晶体中的缺陷和应力增加,拉曼光谱峰位发生红移,光致发光光谱发生猝灭现象。另外,共掺杂样品在室温条件下存在明显的铁磁性,饱和磁化强度随着掺杂量的增加而增强。     

Fe掺杂ZnO纳米球的光学特性

采用微乳液法制备了Fe掺杂ZnO纳米球材料(Zn1-xFexO,x=0.1),利用XRD和TEM对制备样品的结构、形貌进行了表征。在室温下,测得材料宽化的吸收光谱。用325nm的激光激发,测量了ZnO纳米球的光致发光光谱,低强度激发时观察到半峰全宽较窄、峰值波长为385nm的紫光峰和半峰全宽较宽、峰值波长约625nm的深能级发光峰;两峰的发光强度和峰位随着激发光功率密度的变化而变化,但变化规律不同。所合成材料的吸收和发光性质与Fe掺杂相关。     

Fe、Ni共掺杂ZnO基稀磁半导体光学性能与铁磁性研究

采用水热法成功制备了不同掺杂浓度的Zn_1-2xFe_xNi_xO（x=0,0.025,0.05,0.1）稀磁半导体材料,利用X射线衍射（XRD）、透射电子显微镜（TEM）和X射线能量色散分析仪（XEDS）对样品进行表征,并结合拉曼（Raman）光谱、光致发光光谱（PL）和振动样品磁强计（VSM）研究样品的光学性能和磁学性能。结果表明,水热法制备的样品具有结晶性良好的纤锌矿结构,没有杂峰出现,形貌为纳米棒状结构,分散性良好。Fe²⁺、Ni²⁺是以替代的形式进入ZnO晶格中,Fe和Ni的掺杂使得晶体中的缺陷和应力增加,拉曼光谱峰位发生红移,光致发光光谱发生猝灭现象。另外,共掺杂样品在室温条件下存在明显的铁磁性,饱和磁化强度随着掺杂量的增加而增强。     

非晶Si/SiO-2超晶格的制备及其光谱研究

用磁控溅射方法在玻璃基底上制备了非晶Si/SiO2超晶格.利用透射电子显微镜 (TEM) 和X射线衍射技术对其结构进行了分析,结果表明,超晶格中Si层大部分区域为非晶相,局域微区呈现有序结构,其厚度由1.8-3.2nm变化,SiO2层厚度为4.0nm.并采用多种光谱测量技术,如吸收光谱、光致发光光谱和Raman光谱技术,对该结构的光学性质进行了系统研究.结果表明,随纳米Si层厚度的减小,光学吸收边以及光致荧光峰发生明显蓝移,Raman峰发生展宽,即观测到明显的量子尺寸效应.     

非晶Si/SiO2超晶格的制备及其光谱研究

用磁控溅射方法在玻璃基底上制备了非晶Si/SiO₂超晶格.利用透射电子显微镜 (TEM) 和X射线衍射技术对其结构进行了分析,结果表明,超晶格中Si层大部分区域为非晶相,局域微区呈现有序结构,其厚度由1.8—3.2nm变化,SiO₂层厚度为4.0nm.并采用多种光谱测量技术,如吸收光谱、光致发光光谱和Raman光谱技术,对该结构的光学性质进行了系统研究.结果表明,随纳米Si层厚度的减小,光学吸收边以及光致荧光峰发生明显蓝移,Raman峰发生展宽,即观测到明显的量 关键词：     

钴基掺杂氧化物结构特征的研究

利用溶胶-凝胶(sol-gel)法制备出了一系列La0.8Sr0.2Co1-xFexO3样品.xRD结果显示,在La0.8Sr0.2Co1-xFexO3系列样品中,未掺杂的La0.8Sr0.2CoO3样品具有很好的单相结构,并且衍射峰没有发生劈裂;而Fe掺杂的La0.8Sr0.2CoO3样品中几乎每个衍射峰都发生了劈裂,在Fe掺杂的La0.8Sr0.2CoO3样品中可能存在两种不同的晶体结构.利用xANES研究了La0.8Sr0.2Co1-xFexO3样品中Co离子和Fe离子的化合价发现,Fe离子存在两种不同的化合价态,即Fe3+和Fe4+离子,在La0.8Sr0.2Co1-xFexO3样品中形成了两个不同离子的富集区,一个是由Co3+、Co4+和Fe3+等离子组成的,一个是由Fe4+和Co3+、Co4+等离子组成的,因此在Fe掺杂的La0.8Sr0.2CoO3样品中存在两种不同的晶体结构.     

纳米Ce_(1-x)(Fe_(0.5)La_(0.5)x)O_(2-δ)固溶体的水热合成及光谱分析

采用水热方法合成Ce1-x(Fe0.5La0.5)xO2-δ固溶体。利用X射线衍射技术(X-ray diffraction tech-nique,XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合,通过紫外可见漫反射光谱(UV-Vis dif-fraction spectrum)及拉曼光谱(Raman spectrum)表征其电子跃迁性能及由于双离子掺杂所引起的一系列掺杂效应。XRD结果表明,Ce1-x(Fe0.5La0.5)xO2-δ固溶体为CeO2立方萤石结构,当掺杂量增加到x=0.30时出现了微弱的Fe2O3杂相衍射峰;讨论了两种离子在晶格中不同的取代位置。晶胞参数随着掺杂量的增大而逐渐增大,当掺杂量达到x=0.18后保持基本不变。紫外漫反射光谱表明,随着掺杂量的增大,固溶体的带隙吸收边红移,即能隙逐渐减小,Fe离子在CeO2晶格中表现为+3价。Raman光谱F2g振动峰位逐渐向低波数方向移动,同时振动峰逐渐宽化,进一步证明了掺杂离子的影响效应。     

Fe,Co共掺杂ZnO薄膜结构及发光特性研究

采用溶胶凝胶法在玻璃衬底上制备了Fe,Co共掺Zn0.9FexCo0.1-xO(x=0,0.03,0.05,0.07)系列薄膜.通过扫描电镜(SEM)、X射线衍射(XRD)、X射线光电子谱(XPS)和光致发光(PL)谱对薄膜样品的表面形貌、晶体结构、成分和光学性能进行了研究.XRD结果表明所有ZnO薄膜样品都呈六方纤锌矿结构,在样品中没有观察到与Fe和Co相关的团簇,氧化物及其他杂相的衍射峰,表明共掺杂改善了Fe或Co在ZnO的分散性.XPS测试结果揭示样品中Co离子的价态为+2价;Fe离子的价态为+2价和+3价共存,但Fe相对浓度的增大导致Fe3+含量增加.所有样品的室温光致发光谱(PL)均观察到紫外发光峰和蓝光双峰,其中Fe,Co共掺ZnO薄膜的紫外发光峰较本征ZnO出现蓝移,蓝光双峰峰位没有变化,但发光强度有所减弱;而掺杂ZnO薄膜的绿光发光峰几乎消失.最后,结合微结构和成分分析对薄膜样品的发光机理进行了讨论.     

ZnCdTe/ZnTe超晶格的近带边发射特性

本文通过不同激发光强度下的光致发光实验,把Zn0.67Cd0.33Te/ZnTe超晶格(SLs)样品的两个发光谱峰分别归结为与激子有关的和导带电子到受主的辐射复合过程.为进一步了解样品的发光特性,做了不同温度下的光致发光实验,得到了两个谱峰在高温区的激活能,即:高能峰为127meV,低能峰为132meV.     

菱面片层氧化镁的制备及晶格畸变与反常红外特性

以低品位白云石为原料采用二次酸浸、EDTA-氨水沉淀法制备前驱体Mg(OH)2,经煅烧得到菱面片层状多空隙结构的纳米MgO晶体.通过X射线衍射(XRD)、高分辨率扫描电镜(HRSEM) 及傅立叶红外光谱(FT-IR)等测试手段对所得产物的物相和形貌等进行了表征.分析表明:氧化镁为结晶良好、立方晶系,厚度约10～20 nm,最大面积可达1μm2左右的菱形纳米片层结构;XRD数据表明纳米氧化镁的微结构存在晶格畸变并导致XRD相位差发生变化;红外光谱表明,Mg-O键伸缩特征吸收峰向高波数方向移动(蓝移)了约84.82 cm-1,而弯曲特征吸收峰向低波数方向移动(红移)了约31.88 cm-1,并导致红外吸收光谱的宽频化.结合XRD数据分析结果和界面效应等物理现象讨论了反常红外吸收机理.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.