单根六方截面ZnO纳米针制备与发光特性

利用气相传输法,以高纯度氧化锌和碳粉为原料,通过高温碳热还原法制备出可分离单根针状ZnO纳米晶体。用XRD、SEM和PL等手段对其进行了表征。结果表明:样品系沿c轴方向生长、具有六方截面自组装ZnO纳米针(线)晶体。除具有一般线状ZnO纳米晶体相似的紫外光激励的PL谱外,在800nm飞秒激光脉冲激励下,从该样品可观测到上转换紫外受激辐射。     

氩气中飞秒超强紫外激光成丝的实验研究

中心波长808 nm,脉宽70 fs的钛蓝宝石激光系统三倍频后产生的中心波长268 nm、带宽1.5 nm、单脉冲能量0.58 mJ的紫外超快激光光源经凹面镜聚焦后注入到样品池氩气中,由强场非线性效应诱导形成了等离子体通道,并对紫外激光脉冲光谱进行展宽.实验着重研究了268 nm波段的紫外激光成丝特点,以及在不同气体压强、聚焦长度、气体种类等条件下紫外光丝对光谱的调制作用.在2.2×105Pa氩气气压、焦距1000 mm条件下,可以获得光谱宽度3.3 nm,加宽为人射紫外脉冲的2.2倍.实验观察到压强和聚焦长度的增加都有利于等离子体通道的增加,有利于光谱展宽.紫外激光诱导的等离子体通道为在紫外波段内获得极端超快激光脉冲提供了有效的途径.     

1150nm掺镱光纤激光器输出特性实验研究

以光纤光栅对为激光腔、双包层掺镱光纤为增益介质、976nm半导体激光器为泵浦源,研制全光纤化的1 150nm波段长波光纤激光振荡器.在室温下实现了最大平均输出功率为12.7 W的1 150nm波段单模光纤激光输出,激光振荡器的光光转换效率为42.33%.最大功率输出时,激光中心波长为1 150.48nm,光谱的3dB线宽为0.45nm,边模抑制比达38dB.该研究对研制1 150nm波段高功率光纤激光振荡器具有一定的参考价值.     

通过四波参量过程,在钠蒸汽中产生相干可调谐的330nm和333nm辐射

在钠蒸汽中,调谐输入激光波长,使之与钠原子3s—4d双光子跃迁共振,通过四波参量过程产生紫外可调谐的相干辐射。本文报告所产生的330nm333nm相干辐射强度,随钠蒸汽密度、输入基波功率和波长的变化。在平面波近似和紧聚焦条件下,对产生的紫外相干辐射进行了比较。在紧聚焦条件下。产生330nm和333nm的总转换效率为3％。     

特殊变色蓝宝石的紫外-可见光光谱研究

坦桑尼亚Umba出产颜色丰富的刚玉,该研究对象是一颗来自Umba的具有特殊变色效应的蓝宝石,D65光源（色温6 500 K）下呈现淡黄色,A光源（色温2 856 K）下呈现淡紫红色。为了研究这颗变色蓝宝石紫外-可见光光谱中的谱峰归属与变色成因,该研究使用电荷补偿理论来分析此样品紫外-可见光光谱中的谱峰归属。采用紫外-可见分光光度计（UV-Vis）和激光剥蚀电感耦合等离子体质谱仪（LA-ICP-MS）对这颗变色蓝宝石进行了测试。结果发现,变色蓝宝石紫外-可见光光谱中存在位于377,388和450 nm处的3个吸收峰和1个以560 nm为中心的宽缓吸收带。样品的颜色主要受450 nm处吸收峰和以560 nm为中心的吸收带影响,其中以560 nm为中心的吸收带造成了这颗蓝宝石的变色效应。根据激光剥蚀电感耦合等离子体质谱仪的测试结果,样品中主要杂质元素有Fe,Ti,Cr,V和Mg等。样品紫外-可见光光谱中377,388和450 nm处的吸收峰是由Fe3+导致。蓝宝石中的Cr3+,V3+,Fe2+-Ti4+对都可以在560 nm附近产生吸收,结合电荷补偿理论分析,刚玉中的Mg2+会优先和Ti4+进行电荷补偿,样品中Mg含量要稍微高于Ti,推测样品中几乎所有Ti4+会与Mg2+进行电荷补偿,因此样品中几乎不会存在Fe2+-Ti4+对。Fe2+-Ti4+对电荷转移产生的吸收特征具有很强的偏振性,尤其是在580 nm以后的吸收特征会随着偏振方向的改变而有很明显的变化。偏振紫外-可见光光谱测试发现以560 nm为中心的吸收带没有明显的偏振性,进一步验证了样品中几乎没有Fe2+-Ti4+对,因此以560 nm为中心的吸收带主要是由于Cr3+和V3+造成的。样品的颜色主要是由Fe3+,Cr3+和V3+引起的,而变色效应主要是由Cr3+和V3+导致。结合电荷补偿机制与偏振-紫外可见光光谱来解释这颗变色蓝宝石的紫外-可见光光谱中以560 nm为中心的吸收带的归属,为研究刚玉紫外-可见光光谱中较为常见的位于560 nm左右吸收带的归属提供了一种新的研究思路。     

样品温度对激光诱导土壤等离子体辐射特性的影响

为了研究样品温度对激光诱导等离子体辐射特性的影响,以国家标准土壤样品为靶,在空气中利用波长为1 064nm的Nd∶YAG纳秒脉冲激光烧蚀不同温度(≤350℃)下的片状样品,测量了激光诱导等离子体的发射光谱强度和信噪比,计算了光谱分析检出限和信号的测量准确度.实验结果表明,当能量为200mJ时,随着样品温度的升高,等离子体辐射逐渐增强,并且在样品温度为300℃时达到最大值.计算表明,元素Al、Mg、Ba和Fe在300℃样品温度时的光谱线强度比室温条件下分别提高了67%、58%、61%和52%,信噪比分别增大了41%、51%、28%和38%,且元素分析检出限和光谱信号稳定性均有改善.升高样品温度有利于改善激光光谱的质量.     

光子晶体液晶光纤随机激光研究

将掺杂激光染料DCM的手性向列相液晶注入全反射型光子晶体光纤微孔中,研究了激光辐射行为。采用固体Nd∶YAG倍频532 nm激光作为抽运光,室温下,在各个方向上均能探测到随机激光辐射谱。当抽运光的入射方向与样品轴向成30°,光纤光谱仪沿样品轴向方向以及垂直样品轴向方向探测时,在600~650 nm范围内不同波段测得多个离散的尖锐随机激光辐射峰,其线宽约为0.2~0.3 nm。当加热样品至各向同性温度时,激光辐射峰消失。光子晶体光纤的微孔中,作为较强散射介质的手性向列相液晶在不同温度下呈现不同分子取向和折射率分布,这是随机激光产生和关闭的根本原因。     

纳秒激光诱导空气等离子体的红外辐射特性研究

纳秒激光诱导空气等离子体存在从紫外、可见、近红外乃至射频微波的宽谱段辐射,但目前的研究大多关注紫外到可见波段的光谱辐射。激光等离子体作为一种新型的红外辐射源具有很多优势,相比于红外干扰弹以及红外干扰手段而言,空气等离子体红外辐射源可以灵活布置,成本低廉,因此研究空气等离子体的红外辐射特性就很有必要。针对目前脉冲激光诱导空气等离子体的红外干扰研究需要,对激光波长为532 nm的纳秒脉冲激光诱导空气等离子体的红外辐射特性进行实验研究,探讨激光能量对空气等离子体红外辐射强度的影响规律,以及空气等离子体红外辐射的角度分布特性,分析了等离子体红外辐射的可能产生机制。实验结果表明,激光诱导空气等离子体在950～1 700 nm范围内的红外光谱为线状谱和连续谱的叠加。其中线状谱主要是氮和氧的中性原子谱线,并且氮原子红外辐射占主导。随着激光能量的增加,由于空气击穿产生的氧和氮原子数量增加,导致空气等离子体红外辐射的谱线强度逐渐增大。随着红外探测角度的变化,在探测角度为75°时,OⅠ 1 128.63 nm和NⅠ1 246.96和1 362.42 nm谱线强度达到最大,在探测角度为120°时,NⅠ 1 011.46和1 053.96 nm谱线强度达到最大,这是因为空气等离子体红外辐射强度随探测角度变化呈现空间非对称性,表明空气等离子体内不同粒子的空间分布呈现非对称性。     

紫外激发下锰掺杂纳米氧化锌

应用气相传输法, 以铜为催化剂, 在硅衬底上制备了锰掺杂氧化锌纳米四足晶须. 利用x射线与电子衍射谱、扫瞄电镜和高分辨率透射电镜, 对样品形貌、结构和成份进行表征与检测; 通过355nm与375nm紫外光激发下掺杂与未掺杂样品光致发光谱的对比, 结合拉曼散射谱与光致激发谱对掺杂样品中反常光致发光机理进行分析. 结果表明, 样品沿［0001］方向生长的前端和内部长有纤细刺状结构的中空六方管组成; 样品中掺入Mn2+的无辐射复合中心作用, 是掺杂样品紫外辐射强度和谱宽变小的主要原因, 氧化锌晶体中晶格周期对Mn2+中d-d电子跃迁过程的影响, 是375nm紫外光激发下掺杂样品中415nm辐射峰产生的主要原因.     

用于355nm紫外激光器的消偏振二向色镜

采用离子束辅助电子束成膜,用双重膜厚监控方法监控各膜层厚度,制备了45°入射、808nm高反、1064nm高透的消偏振二向色镜,并用于全固态355nm激光器.将部分薄膜样品在250℃进行退火处理后,用Lambda950分光光度计测试该样品的光谱性能;用表面热透镜技术测量退火前后该样品的弱吸收值;用激光阈值损伤装置测试该样品在1064nm调Q激光下的损伤阈值;用NIKON显微镜观察样品在不同激光能量辐照下的破斑形貌.实验结果表明:波长为808nm和1 064nm时,薄膜透射率分别为0.04%和99.6%,符合设计要求,满足全固态355nm紫外激光器系统所要求的光学性能指标;退火后的弱吸收值较退火前有所降低;在激光作用下薄膜产生微破坏喷出,说明膜层不会向灾难性破坏演变.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

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.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

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.     

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.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.