基于受激发光实验的生物光尾流特性

 基于生物受激发光与流场机械刺激间的相关性,构建了库埃特流场刺激下的生物受激发光实验平台,分析了影响生物发光的水动力因素剪应力。实验结果显示：引起多边膝沟藻受激发光的剪应力阈值为0.1 N/m²;当流场中的剪应力大于发光阈值后,生物发光强度随着剪应力的增大而增强。采用FLUENT软件模拟计算了不同航速下某潜艇尾流场中的剪应力,计算结果表明：剪应力随着尾流长度的增加而减小,在近场区域剪应力出现了类似正弦波振荡的减小,且航速越大减幅越大,减速越快;当潜艇航速大于4.1 m/s航行时, 2 000 m处尾流的剪应力仍然大于引起生物发光的剪应力阈值。     

流场刺激下海洋生物发光的光学特性及数理模型

生物受激发光探测是一种感知水中目标的新技术、新手段。选取多边膝沟藻、夜光虫和月芽形梨甲藻3种典型海洋受激发光生物体为对象,采用光谱仪、光子计数器、库埃特流场旋转圆筒等装置搭建了生物受激发光实验平台,研究了不同刺激下生物体受激发光的光学特性,并在此基础上结合概率论和数理统计理论,建立了流场刺激下的生物发光的数理模型。结果表明:发光藻的发光具有较好的单色谱特性,峰值波长集中在472 nm左右,谱线的半波宽度为30～40 nm。发光藻的发光随着机体的疲劳而变弱,但发光能力随着机体的休息会慢慢恢复。同种刺激条件下,3种藻发光强度的强弱依次为月芽形梨甲藻、夜光虫、多边膝沟藻。     

相敏检测调制深度对受激拉曼信号强度及信噪比影响研究

受激拉曼散射是相干拉曼散射中的一种，其产生的信号在三阶非线性效应下得到了显著地增强，且没有非共振背景的干扰，光谱与自发拉曼光谱几乎完全一致。因此，基于受激拉曼散射的显微成像技术具有无标记、高特异性、非侵入等优点，已成功运用在生物细胞成像中并取得了许多重大的成就。受激拉曼信号与激发光的波长相同，易受到激发光背景噪声的干扰，为解决该难题，常采用光学调制与相敏检测相结合的方法对其进行检测。检测过程中，调制深度对受激拉曼信号强度和信噪比有重要影响。针对此，基于相关理论深入分析了调制深度对受激拉曼信号强度及信噪比的影响。同时考虑到在生物光谱成像等应用中，细胞光损伤阈值对两束激发光功率之和的限制，分析了不同调制深度下，获取最大信号强度及最佳信噪比的激发光功率配置方法。通过搭建受激拉曼实验系统，以二甲基亚砜为研究对象，进行实验验证。研究结果表明，在光损伤阈值的限制条件下进行受激拉曼损耗检测时，同一调制深度下，当泵浦光与斯托克斯光光功率比为1:1时信号强度达到最强，比值为1∶2时信号的信噪比达到最佳。在泵浦光与斯托克斯光光功率比相同的条件下，受激拉曼信号强度和信噪比均随调制深度的降低而降低且近似呈线性...     

船舶噪声激励夜光虫发光特性实验研究

对船舶噪声刺激下的生物发光特性展开研究,发光生物为夜光虫。利用声学换能器模拟船舶辐射噪声,在含有发光生物夜光虫的实验水槽中进行生物发光实验。声学换能器发出不同频率,对夜光虫受不同频率噪声激励下的发光特性进行记录。通过对不同激励频率下夜光虫发光图像的分析处理,得到不同频率激发下生物发光点图像,经统计分析得到了夜光虫在船舶噪声激励下的发光特性,得出夜光虫发光点数随频率和声源级的增加而增加的结论。     

强激光长程传输中受激拉曼散射对光束特性的影响

依照受激拉曼散射(SRS)半经典理论从物质激发感应出的三阶非线性极化率X~(3)出发,在强激光长程传输受激拉曼散射中建立了泵浦(传输)激光相位与斯托克斯(Stokes)光强相耦合的理论模型。它清楚地说明了SRS效应影响泵浦激光光束特性,其中包括时间特性及空间特性(光束质量)的物理机制及影响因素。理论分析与实验结果符合得较好。实验还测得了不同转换效率η_s情况下传输后的泵浦光及Stokes光的时间过程特性。结果表明,在小转换效率的条件下,泵浦光时间特性基本不受SRS效应的影响;而当转换效率η_s>5％时,泵浦光脉宽随η_s增大而被逐渐压缩。     

共轭聚合物中受激吸收与受激辐射的量子动力学研究

基于扩展的一维SSH紧束缚模型结合非绝热的分子动力学方法,理论研究了共轭聚合物分子(PPV)在光脉冲作用下受激吸收和受激辐射的量子动力学过程.首先,设定分子初始处于基态,讨论了受激吸收过程中不同的电子受激跃迁模式与光激发脉冲的关系.通过对终态的分析,发现分子受激后只能产生电子-空穴的束缚态,包括:激子、双激子和高能激子.计算了各种激发态的产率,特别是,给出了各种激发态产率与光激发能量的定量关系.此外,基于实验,分别讨论了光激发强度对高能激子和双激子产率的影响,并与实验结果进行了比较.最后,设定分子初始分别处于激子和双激子态,研究了分子内定域能级之间的受激辐射过程,并简单讨论了激子和双激子受激辐射与光激发能量及强度的关系.     

一种独立于激发光脉冲参量的磷光寿命测量方法

脉冲法磷光寿命测量中，激发光脉冲参量（脉冲宽度和形状）、用于磷光强度衰减分析的起始时刻的选取是影响寿命计算准确度的关键因素。以线性时不变系统理论为依据，探讨了磷光强度衰减特性与激发光脉冲参量之间的关系，发现对于有限宽度的激发光，激发光脉冲消失之后的磷光强度衰减特性独立于激发光脉冲参量；选取激发光脉冲消失时刻作为磷光强度衰减分析的起始时刻，可获得准确的寿命计算。利用磷光探针氧卟啉（Oxy-PhorR2）标准试样做了针对性实验，实验结果验证了理论的正确性。     

水体参数对受激布里渊散射阈值及增益的影响

受激布里渊散射在激光雷达海洋遥感领域具有广泛应用,而水体参数变化对其阈值及增益等关键特征参数影响的研究还很缺乏.本文利用分布式噪声模型及耦合波方程,理论分析了水的温度、压强和衰减系数对受激布里渊散射阈值和增益系数的影响.在理论分析基础上,设计了一种温度压强可控实验系统,采用平均衰减系数法实验测量了不同温度、压强及衰减系数下的阈值和增益系数.结果表明,受激布里渊散射阈值随压力和衰减系数的增大而增大,随温度的升高而减小,而增益系数则呈现与阈值相反的变化趋势.温度和衰减系数对阈值和增益系数的影响大于压力.研究结果对受激布里渊散射激光雷达海洋遥感探测具有重要意义.     

混沌光在光纤中的布里渊散射光特性

分析了混沌光注入功率和单模光纤长度对布里渊散射斯托克斯光线宽的影响,发现随着注入混沌光功率的增大,斯托克斯光线宽逐渐减小;当注入的混沌光功率达到一定值时,斯托克斯光线宽几乎不变。分析了注入混沌光功率和单模光纤长度对后向散射功率的影响,发现当注入混沌光功率一定时,后向散射功率随着光纤长度的增加而迅速增大,当光纤长度超过15.41 km时,后向散射功率趋于饱和。讨论了混沌受激布里渊散射光阈值的影响因素,结果表明,混沌受激布里渊散射光阈值很高,比传统的连续光注入光纤产生的受激布里渊散射阈值高约19 d B。     

单模石英光纤受激拉曼散射温度特性研究

研究了在不同温度下单模石英光纤的受激拉曼散射光谱,从实验和理论上分析了温度对拉曼散射光谱特性的影响,在脉冲调Q倍频YAG激光的泵浦作用下,获得了石英光纤一级斯托克斯光的拉曼频移、带宽及光强随温度的变化规律。实验表明随着温度的升高,拉曼频移逐渐增大,在一定的温度范围内拉曼频移和温度成线性关系。在相同的泵浦功率作用下,当温度较低时,拉曼光谱的级次较低, 低温对高阶斯托克斯光有抑制作用; 温度越低其阈值越高;而拉曼光谱的谱线宽度随温度的变化不是线性的,存在一个谱线宽度极大值点。理论和实验表明温度对光纤受激拉曼散射的光谱特性有直接的影响。     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

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.     

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.