KDP晶格振动模和生长机制的拉曼光谱研究(英文)

用空间群理论分析和指认了KDP晶体的拉曼活性晶格振动模 ,测量了晶体以及生长溶液的拉曼光谱 ,重点分析了出现在固 /液界面附近的 91 6cm- 1拉曼峰 ,该峰被指认为扭曲的P(OH) 2 集团反对称伸缩振动。依据本文的理论分析和实验测量 ,我们认为H2 PO- 4阴离子集团的二聚物可能是KDP晶体的生长基元。     

偏磷酸盐掺杂对KDP晶体生长与光学性能的影响

研究了KDP晶体中散射颗粒形成的一种机理。掺杂微量偏磷酸盐即可使KDP晶体中出现散射颗粒，随着掺杂浓度提高，散射颗粒密度增大。散射颗粒形成的原因在于偏磷酸根具有PO4四面体端基，在晶体生长时容易被生长晶面吸附进入晶格。偏磷酸盐掺杂影响了晶体的光学性能，晶体的光损伤阈值也明显地爱到掺杂的影响。     

氘化对KH2PO4晶体微观缺陷影响的正电子湮没研究

采用传统降温法从不同程度氘化(x=0, 0.51, 0.85)的生长溶液中生长氘化KH₂PO₄(KDP) 晶体, 利用正电子湮没技术(正电子寿命谱和多普勒展宽谱)、结合X射线衍射谱(XRD) 结构分析, 对KDP晶体氘化生长的微观缺陷进行了研究, 讨论了氘化程度对晶体内部微观结构特性、缺陷类型和浓度的影响. XRD结果显示晶胞参数a, b值随氘含量的增加而增加, c值无明显变化; 正电子寿命谱结果发现随着氘化浓度的提高, KDP晶体内部中性填隙缺陷以及氧缺陷不断增加, 引起晶体晶格畸变; 氢空位、K空位、杂质替位缺陷不断发生缔合反应形成复合缺陷, 缺陷浓度不断减少; 团簇、微空洞等大尺寸缺陷也在不断发生聚合反应, 缺陷浓度表现为不断减少. 多普勒实验结果表明随着氘化程度的提升, 晶体内部各类缺陷表现为同步变化. 实验结果表明, KDP晶体在低浓度氘化生长(50%以内)下缺陷反应较弱, 而在高浓度氘化(50%以上)下的缺陷反应显著增强.     

KDP晶体中点缺陷Na取代K的电子结构研究

 对磷酸二氢钾(KDP)晶体中Na取代K点缺陷的几何结构及电子结构进行了第一性研究。计算的形成能约为0.46 eV,因此在KDP晶体中此类缺陷比较容易形成。Na取代K以后没有在带隙中形成缺陷态,但在价带中引入两个占据态。它们分别位于费米面以下49 eV和21.5 eV处,这两个占据态分别由Na原子的s和p轨道形成。相对于K来说,由于它们位于价带深处,具有很低的能量,因此Na在KDP中比K稳定。Na在KDP晶体中与周围氧原子的重叠布居仅为0.09, 故它不与主体原子发生共价作用,仅以静电库仑力影响周围原子,此缺陷周围晶格仅发生微小畸变。     

机械夹持状态下KDP晶体的热应力

从机械结构角度对机械夹持状态下吸收了高能激光束能量的磷酸二氢钾(KDP)晶体内部产生热应力的问题进行了研究。理论分析了KDP晶体吸收激光能量引起的温升,研究了机械夹持状态下KDP晶体内部热应力的生成机理。采用有限元方法对KDP晶体的温度分布和热应力分布进行了仿真计算,分析了夹持装置结构参数、预紧力、摩擦系数和弹性模量对热应力的影响。结果表明,夹持装置对KDP晶体的机械夹持作用是KDP晶体内部产生热应力的重要因素,热应力的大小与夹持装置的结构参数有关。     

夹持方式和加工误差对大口径薄型KDP晶体附加面形的影响

惯性约束聚变频率转换系统中,大口径薄型KDP晶体的面形质量是影响频率转换效率能否达到设计要求的关键因素之一。针对45放置状态下口径为400 mm400 mm的三倍频KDP晶体,采用ANSYS有限元分析软件,建立了不同夹持方式和具有不同加工误差的KDP晶体模型和夹具模型,分析了加工误差对不同夹持方式下KDP晶体附加面形的影响,给出了不同加工误差和不同夹持情况下,KDP晶体附加面形的P-V值和RMS值。研究结果表明,夹持方式和加工误差是引起KDP晶体附加面形变化的重要因素,正面压条夹持方式即使在晶体和夹具存在加工误差时也可以较好地控制晶体的附加面形。     

加工误差引入的薄型KDP晶体附加面形

针对惯性约束聚变（ICF）驱动装置中口径为400 mm400 mm薄型频率转换KDP晶体在45放置状态下产生的附加面形问题,采用有限元分析软件ANSYS,建立了以实测数据为基础的大口径薄型KDP晶体的应变模型和有加工误差的夹具模型,仿真分析了KDP晶体的加工误差和夹具的加工误差对KDP晶体附加面形的影响, 给出了KDP晶体附加面形变化的P-V值和RMS值。在此基础上,通过对KDP晶体的加工误差及夹具支撑表面不同类型和不同大小加工误差的分析和比较,得出:KDP晶体边缘的加工误差和夹具支撑表面的凹型加工误差是引起较大附加面形的原因之一,KDP晶体的加工误差也会导致其面形变化不均匀,而夹具支撑表面的凸型、波浪形加工误差和压条表面的随机加工误差对KDP晶体附加面形的影响相对较小,且支撑表面的随机加工误差引起的附加面形变化介于其他两者之间。     

加工误差引入的薄型KDP晶体附加面形

针对惯性约束聚变（ICF）驱动装置中口径为400 mm400 mm薄型频率转换KDP晶体在45放置状态下产生的附加面形问题,采用有限元分析软件ANSYS,建立了以实测数据为基础的大口径薄型KDP晶体的应变模型和有加工误差的夹具模型,仿真分析了KDP晶体的加工误差和夹具的加工误差对KDP晶体附加面形的影响, 给出了KDP晶体附加面形变化的P-V值和RMS值。在此基础上,通过对KDP晶体的加工误差及夹具支撑表面不同类型和不同大小加工误差的分析和比较,得出：KDP晶体边缘的加工误差和夹具支撑表面的凹型加工误差是引起较大附加面形的原因之一,KDP晶体的加工误差也会导致其面形变化不均匀,而夹具支撑表面的凸型、波浪形加工误差和压条表面的随机加工误差对KDP晶体附加面形的影响相对较小,且支撑表面的随机加工误差引起的附加面形变化介于其他两者之间。     

KDP晶体全口径最佳入射角优化方法

根据正交偏振干涉测量法(OPI)获得的KDP晶体折射率的空间分布数据求解KDP晶体内部失谐角分布,进而建立了倍频及和频KDP晶体全口径最佳入射角的优化模型和方法。分析讨论了不同折射率畸变程度和不同功率密度入射情况下倍频及和频晶体入射角的变化规律。在此基础上,对KDP晶体的全口径最佳入射角进行了优化。结果表明:当KDP晶体折射率畸变程度较大时,倍频晶体对折射率变化较为敏感,而和频晶体对折射率变化则相对不敏感。在实际工作中,首先在假设倍频晶体折射率分布均匀的前提下,对和频晶体的最佳入射角进行优化,而后通过适当调整倍频晶体及和频晶体的入射角,最终确定倍频晶体及和频晶体的全口径最佳入射角。     

KDP晶体全口径最佳入射角优化方法

根据正交偏振干涉测量法(OPI)获得的KDP晶体折射率的空间分布数据求解KDP晶体内部失谐角分布,进而建立了倍频及和频KDP晶体全口径最佳入射角的优化模型和方法。分析讨论了不同折射率畸变程度和不同功率密度入射情况下倍频及和频晶体入射角的变化规律。在此基础上,对KDP晶体的全口径最佳入射角进行了优化。结果表明：当KDP晶体折射率畸变程度较大时,倍频晶体对折射率变化较为敏感,而和频晶体对折射率变化则相对不敏感。在实际工作中,首先在假设倍频晶体折射率分布均匀的前提下,对和频晶体的最佳入射角进行优化,而后通过适当调整倍频晶体及和频晶体的入射角,最终确定倍频晶体及和频晶体的全口径最佳入射角。     

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.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

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.     

Sorting of bending magnets for the SSRF booster

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.     

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.