外电场下二氧化硫的分子结构及其特性

以6-311++g(3d, p)为基组, 采用B3P86方法研究了不同外电场(-0.04-0.04 a.u.)对SO₂分子基态的几何参数、电荷分布、能量、电偶极距、最高占据轨道(HOMO)能级、最低占据轨道(LUMO)能级及能隙的影响, 在优化构型的基础上, 采用含时密度泛函(TD-B3P86)方法研究了SO₂分子在外电场作用下前9个激发态的激发能、跃迁波长和振子强度. 研究表明: SO₂的几何参数与电场强度大小及方向均有明显的依赖关系. 电场由-0.04 a.u. 变化至0.04 a.u.时, 体系的总能量先增加后减小; 偶极矩先减小后增加; HOMO能级一直减小; LUMO能级先增加后减小; 能隙先增加后减小. 激发态的激发能、跃迁波长和振子强度与电场关联均较为复杂, 说明SO₂的激发特性易受外电场影响.     

一氟二氯乙烷分子在外电场中的光谱特征和解离特性

利用密度泛函理论在B3LYP/6-311+G(d, p)水平上研究不同外加电场下(-0.05～0.05 a.u.)一氟二氯乙烷分子的光谱特征和解离特性,其中包括该分子基态结构、总能量、偶极矩、最高占据轨道能级、最低空轨道能级、能隙、红外光谱、拉曼光谱、紫外可见光吸收光谱及C原子与Cl原子间势能曲线等数据在电场下的变化趋势。在y轴方向上,随着负向电场的增强,C原子与Cl原子核间距增长、最高占据轨道能级减小,体系总能量、最低未占据轨道能级、能隙先增大后减小,偶极矩先减小后增加。外加电场会影响一氟二氯乙烷分子红外光谱、拉曼光谱与紫外可见光吸收光谱的吸收强度和吸收峰频率,红外光谱、拉曼光谱与紫外可见光吸收光谱随着电场变化出现红移或蓝移现象。C原子与Cl原子间势垒随着负向电场增加逐渐减小,并在电场达到-0.05 a.u.时C原子与其中一个Cl原子发生断裂,当分子中一个C—Cl键断裂后,施加强度为-0.04 a.u.的电场时另外一个C—Cl键发生断裂,分子在电场下发生逐步解离,研究结果完善了一氟二氯乙烷分子受外电场影响的理论数据。     

特殊构型Si_2N_2分子团簇电致激发特性的密度泛函理论研究

以在可见光区有吸收峰的Cs构型的Si2N2分子团簇为研究对象,利用密度泛函B3LYP方法,在aug-ccpVTZ基组水平下优化得到了处于不同外电场中的Si2N2分子团簇的稳定结构.分析发现:在不同的外电场中,Si2N2分子构型对称性没有发生改变,均为Cs对称性,且都有6种振动模式;随着外电场强度的逐渐增大,Si2N2分子振动频率较低的前三种振动模式的频率略有减小,而后三种振动模式的频率逐渐增加;随着外电场强度的逐渐增大,在一定电场范围内最高占据分子轨道与最低空分子轨道的能隙值出现振荡,之后能隙值随着外电场强度的增大而减小.在此基础上,采用含时密度泛函TD-B3LYP方法研究了外电场对Si2N2分子吸收谱的影响规律.计算得到的吸收谱范围在紫外-可见光区,这与实验值相符合.随着外电场强度的逐渐增大,在可见光区吸收谱发生红移,最大跃迁振子强度逐渐增大.结果表明,施加外电场有利于Si2N2分子在可见光区的吸收,也有利于操控分子特定激发态的电子状态,进而调节相应的跃迁光谱特性,可达到获得所需特定波长的要求.     

外电场下二氧化锆的分子结构及其特性

对O原子采用6-311++G*基组,Zr原子采用aug-cc-pVTZ-PP基组,利用密度泛函(B3P86)方法优化得到了ZrO2分子的稳定构型,并研究了不同外电场(0—0.025 a.u.)作用下ZrO2基态分子键长、能量、电荷分布、偶极矩和能级的变化规律.在优化构型的基础上,利用含时密度泛函(TD-B3P86)方法研究了ZrO2分子在外电场作用下前6个激发态的激发能、跃迁波长和振子强度的激发特性.研究结果表明:随着电场强度的增大,Zr—2O的键长增大,而Zr—3O的键长均匀减少,总能量降低,偶极矩增大;最高占据轨道能量基本保持不变,最低未占据轨道和能隙均减小.电场的增大使得激发能减小,各个激发态跃迁波长均发生不同程度的红移现象,因而,利用外电场可以控制ZrO2的发光光谱范围在可见-红外区域扩展.     

外场下SnS分子结构及其特性

对S原子采用6-311++G**基组,Sn原子采用SDB-cc-pVTZ基组,利用密度泛函(B3P86)方法对SnS分子进行了基态结构优化,并研究了外场作用下SnS基态分子键长、能量、能级分布、电荷布居分布、谐振频率和红外谱强度的影响规律.然后利用含时密度泛函(TD-B3P86)方法研究了SnS分子在外场下的激发特性.结果表明,在所加的电场范围内(-0.04 a.u.-0.04 a.u.),随着正向电场的增大,分子键长和红外谱强度均是先减小后增大;总能E,SnS基态分子的最高已占据轨道能量EH和谐振频率均是先增大后减小;分子的最低未占空轨道能量EL和能隙Eg均随正向电场的增大而减小.随着正向电场的增大,SnS分子由基态至前9个单重激发态跃迁的波长增大,激发能则减小.     

外电场作用下黄曲霉素B1的分子结构和光谱

利用密度泛函（DFT）理论,在B3LYP/6-311G基组水平上研究外电场（0~0.015 a.u.）作用下黄曲霉素B₁（Aflatoxin B₁,AFB₁）分子的总能量、偶极矩、键长、HOMO-LUMO能隙、红外光谱.在优化构型的基础上,利用含时密度泛函（TDDFT）方法研究紫外可见吸收光谱和激发态的变化.结果表明：在CO键方向上加电场,外电场逐渐增大时,AFB₁分子的总能量逐渐增大,偶极矩逐渐减小.电场对不同的键长影响不同.能隙随外电场逐渐增大而减小,红外光谱吸收峰出现红移或蓝移,紫外可见吸收光谱的两个吸收峰发生不同的移动,但总的谱线集中在近紫外光区.分子各个激发态的激发能在外电场逐渐增大时逐渐减小,表明分子结构越来越不稳定.     

外电场作用下N2O分子的结构与光谱特性

采用密度泛函B3LYP方法,在6-311+g(d)基组水平上研究了不同外电场对直线型分子N₂O的基态结构、偶极矩、轨道能级、红外和拉曼光谱特性的影响,并采用杂化CIS方法研究了N₂O分子在外电场作用下前9个激发态的激发特性.结果表明:外电场导致分子键长变化,但并没有改变分子的直线特征,偶极矩和分子总能量随外电场的增加先减小后增大,而能隙随外电场的增加先增大后减小,外电场的增加使LUMO(lowest unoccupied molecular orbital)组成由π~*轨道变为σ~*轨道,外电场使红外光谱发生移动,峰的强度增强或减弱.外电场的增加显著影响了N₂O分子的激发特性.激发能、激发波长受外电场影响发生了变化,同时,振子强度受外电场影响明显,禁阻跃迁变为可允许的跃迁,允许的跃迁在电场作用下变为禁阻跃迁或者跃迁变弱.紫外光谱在电场的作用下吸收峰发生了明显的移动,而且有新的吸收峰产生.     

外电场下L-茶氨酸分子的结构特征与光谱性质

L-茶氨酸(N-乙基-L-谷氨酰胺)是一类具有降压、抗氧化的非蛋白氨基酸,研究外场下它的结构和光谱特征有助于人们更好地认识L-茶氨酸分子的性质.基于密度泛函理论,利用B3LYP方法,在6-311g(d,p)基组水平上对L-茶氨酸分子进行几何构型优化,在此基础上计算L-茶氨酸分子在不同外电场下(0～0.0125 a.u.)的分子各键长与振动频率,得到对应的红外光谱.同时,在相同的基组下采用含时密度泛函方法(TD-DFT)计算外电场对分子的激发态、前线轨道和能隙的影响.结果表明:分子结构及其紫外、红外光谱都随外电场强度发生变化.随外电场的增加,伸缩振动频率红移,弯曲振动频率蓝移;最高占据轨道的能量(E_(HOMO))与最低空轨道的能量(E_(LUMO))发生改变,前线轨道能隙先小幅增加后随电场减小,分子活性先减小后增强;紫外吸收光谱先蓝移后红移.本研究对L-茶氨酸分子的检测、合成及其生物活性的研究可提供理论依据.     

外电场下L-茶氨酸分子的结构特征与光谱性质

L-茶氨酸(N-乙基-L-谷氨酰胺)是一类具有降压、抗氧化的非蛋白氨基酸,研究外场下它的结构和光谱特征有助于人们更好地认识L-茶氨酸分子的性质.基于密度泛函理论,利用B3LYP方法,在6-311g(d,p)基组水平上对L-茶氨酸分子进行几何构型优化,在此基础上计算L-茶氨酸分子在不同外电场下(0～0.0125 a.u.)的分子各键长与振动频率,得到对应的红外光谱.同时,在相同的基组下采用含时密度泛函方法(TD-DFT)计算外电场对分子的激发态、前线轨道和能隙的影响.结果表明:分子结构及其紫外、红外光谱都随外电场强度发生变化.随外电场的增加,伸缩振动频率红移,弯曲振动频率蓝移;最高占据轨道的能量(E_(HOMO))与最低空轨道的能量(E_(LUMO))发生改变,前线轨道能隙先小幅增加后随电场减小,分子活性先减小后增强;紫外吸收光谱先蓝移后红移.本研究对L-茶氨酸分子的检测、合成及其生物活性的研究可提供理论依据.     

外场作用下蒽分子的激发特性研究

蒽(anthracene)具有良好的热稳定性以及较高的荧光量子产率的优点, 是最早用于研究有机发光器件(organic light-emitting device, OLED)的材料之一. 在本文中, 主要利用量子化学方法研究了不同外电场对蒽分子激发特性的影响规律. 首先采用密度泛函理论(density functional theory, DFT)在6-311G(d, p)基组水平上对蒽分子基态结构进行优化, 基于稳定基态结构, 利用含时密度泛函(time-dependent density functional theory, TDDFT)以及同一基组水平, 计算出蒽分子的前十个激发态的激发能、跃迁偶极矩、振子强度和紫外吸收光谱等数据. 然后以密度泛函B3P86方法优化出的不同外电场下蒽分子基态结构为基础, 使用TDDFT方法研究了不同外电场对蒽分子前线轨道能级和激发特性的影响规律. 结果显示, 无场时蒽分子在紫外区域234.50 nm处有一个较强的吸收峰, 对应基态电子跃迁至第5激发态吸收光子波长; 在外电场作用下, 蒽分子电子由基态跃迁到激发态的各项光谱参数均有显著变化, 加场后蒽分子的吸收光谱发生了红移, 由紫外波段移向了紫外–可见光波段, 与实验值相符合. 分子前线轨道的计算结果也表明蒽分子的最高占据轨道(highest occupied molecular orbital, HOMO)和最低未占据轨道(lowest unoccupied molecular orbital, LUMO)能量差值在不同电场下存在差异. 关键词： 蒽 外电场 激发特性     

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.