高动态范围激光焦斑测量数学模型研究

提出了一种高动态范围的激光焦斑测量方法.首先,构建纹影测量远场焦斑数学模型,确定重构需要的参数,并使用准直光路对参数进行标定;其次,运用综合诊断快速自动准直系统使纹影小球遮挡住旁瓣光斑中心,获得准确的旁瓣光斑;最后,改进计算纹影小球中心及图像融合等方面的纹影重构算法,克服了传统纹影重构方法中主瓣旁瓣中心误差大、合并图像拼接边缘台阶明显的缺点.对大型激光装置参数测量综合诊断系统的远场焦斑测量应用表明:通过对纹影测量远场焦斑数学模型中参数的精确标定以及对纹影重构算法的优化,能够实现高动态范围激光焦斑的准确测量.     

激光远场焦斑测试技术研究

激光远场分布测量一直存在两方面的困难：一方面是由于波面畸变具有不确定性，使得焦平面位置不易确定；另一方面是焦斑“主瓣”和“旁瓣”光能密度相差悬殊，无如此大动态范围的探测器。此文针对现有的激光远场测试的3种常用方法(长焦距透镜法、列阵相机法、Rame Pair法)进行了实验研究。首先需要建立一个实验平台，3种激光远场测试方法在相同的测试条件下对激光束的相同位置进行测试，以减少比对误差。光路排布如图1所示。图1中虚线所包围的部分即3种测试方法的光路排布，由这3种方法分别测得的焦斑和焦斑列阵并通过一定的算法重构焦斑，所得结果比对如图2。     

强激光远场焦斑重构算法研究

 通过CCD图像采集单元结合传统的列阵相机测量高功率固体激光器的远场焦斑分布，采用图像处理技术的边缘算子提取焦斑的几何中心，提出通过几何中心对心的焦斑嵌套重构算法，解决了光斑饱和时的对心难题，实现了快捷准确测量激光焦斑，为激光器的实时控制提供参考数据。     

纹影法测量远场焦斑实验研究

 报导了用纹影法测量远场焦斑的实验结果。远场焦斑经成像透镜放大成像后,由12bit,1 024×1 024面阵科学级CCD相机采集。将一定大小的小球放置在焦斑位置,用以遮挡光斑中心,控制CCD前的衰减可得旁瓣信息,将其与无遮挡光斑拼接,得到焦斑相对强度的完整分布。该方法扩展了焦斑光强测试的动态范围,可探测焦斑约4个量级的光能密度分布,提高了焦斑的测量精度。     

激光惯性约束聚变驱动器终端光学系统中束匀滑器件前置的条件研究

对激光惯性约束聚变（ICF）驱动器终端光学系统中连续相位板（CPP）的位置优化进行了研究.根据高强度激光非线性及微扰传输理论计算了CPP前置时激光通过频率转换系统以后的近远场光束特性和系统的三倍频转换效率.研究发现,前置于基频光路的CPP对三倍频转换效率和出射光束特性均有影响,但只要远场圆形焦斑直径小于05 mm,三倍频转换效率的下降与出射光束通量对比度的上升均在容许范围之内,同时远场焦斑形态和能量集中度也符合设计要求.对于实现远场小焦斑匀滑的CPP前置于ICF的基频光路中进行光束匀滑和整形,不会对IC 关键词： 连续相位板 束匀滑元件 惯性约束聚变 光束通量对比度     

激光能量叠加过程中对准精度对焦斑的影响

利用多光束激光输出耦合叠加是一种提高激光器输出功率的有效方法。采用两束矩形激光对准系统,分析两光束不同对准情况下的焦斑特性。完全对准的情况下,两束光的远场焦斑重合在一起,焦斑能量是两光束能量之和。在实际光束对准系统中,讨论了三种常见的对准误差,并比较了这些误差对焦斑特性的影响。利用ZEMAX软件对设计系统进行了模拟分析,并进行了实验验证。结果表明,元件的位置误差会使远场焦斑能量集中度降低,焦斑半径增大。     

正交光楔激光远场焦斑测量方法

为验证正交光楔激光远场焦斑测量方法在提取光斑高频组分、扩展CCD测量动态范围和减小光束质量测量误差等诸方面的有效性,以常用的光束质量因子作为衡量新方法有效性的指标,建立离焦光斑强度分布理论模型并搭建相应的实验平台进行实验验证。验证结果表明:新方法与传统远场测量方案相比,使实验所用CCD的测量动态范围拓展了约9倍,实际光斑远离中心主核区域的大量高频旁瓣分布特征从CCD背景噪声起伏中凸显出来,光束质量因子的测量平均相对误差也有约16%的精度改善。     

高动态范围激光等离子体诊断系统及其在惯性约束聚变实验中的应用

基于高功率激光等离子体X射线辐射谱特性,设计和研制了一种大画幅高动态范围MCP选通型分幅相机. 单画幅宽度13mm,长度36mm,曝光时间0.5—5ns可调.与X射线CCD比较,系统在1.0—10keV的谱响应相对平整,无高能增强效应.利用高功率激光打靶实验进行了性能考核实验,结果表明,系统的信噪比明显好于X射线CCD系统,动态范围大于3×10³. 系统已经在神光Ⅱ装置ICF物理实验中获得成功应用. 关键词： 动态范围 谱响应 激光等离子体诊断 分幅相机     

飞秒激光产生的X射线双光谱成像

在微介观诊断中往往因为空间限制,选择具有亮度高、单色性好、对比度强的特征谱线,而忽略了轫致辐射谱线。率先实验设计了特征谱线和轫致辐射谱线的双光谱诊断X射线光源的方法,在中国工程物理研究院“星光Ⅲ”激光装置飞秒激光束靶室上进行实验,激光功率密度大于1.6×1018 W/cm2,脉宽为30 fs,45°入射靶面。在入射靶前侧,设计了用于特征光谱成像的针孔成像光路,获得Cu纳米颗粒靶产生的特征X射线的焦斑图像,为76 μm,大于刃边方法测得半径为54 μm的焦斑。在靶后侧,设计了轫致辐射成像光路,利用PIX射线CCD获得2×5的圆形Ta组图像。实验表明,利用双光谱成像设计合理,适合微介观材料动态诊断,提高诊断效率。     

光纤组束激光对可见光硅CCD的有效干扰距离分析

为了分析光纤组束激光对可见光硅CCD的有效干扰距离,对组束激光功率及可见光CCD的饱和阈值进行了分析。在弱湍流和热晕条件下对组束激光的远场功率密度进行了数值计算,计算结果表明该条件下组束激光对可见光CCD的有效干扰距离达到10km左右,组束激光是未来实施光电干扰的又一有效途径。     

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.