被散射介质遮挡目标的相干衍射成像实验

激光照明条件下,可以利用相干衍射成像方法重建被照明物体的清晰图像。按照传统方法,若物体被散射介质遮挡,则需要提前标定或者引入全息实验中使用的参考光才能重建清晰的图像。我们提出了一种线性模型,即使存在散射层的干扰,仍旧能够通过实验获得的功率谱重建被遮挡物体,而无需预先标定。实验结果表明,该方法利用傅立叶变换的精确功率谱图像可以快速收敛至唯一正确的重构解,重建隐藏物体的清晰图像。     

激光等离子体中相干Thomson散射的实验研究

在“星光II”装置上进行了相干Thomson散射实验。实验中以0.35μm激光为作用束,以0.53μm激光作为探针光束,散射光采用反射式收光系统配光谱仪、条纹相机和CCD记录,得到较高时间和空间分辨散射光谱,分析得出时间变化的激光等离子体参数和ui。     

磁逆多光子非线性Compton散射的谱功率

相对论电子在强磁场中的磁逆Compton散射是一种重要的γ射线辐射机制。虽然对该问题的研究已有二十多年的历史，但对磁逆多光子非线性Compton散射谱功率的研究尚未见报道。本文采用电子与光子非弹性碰撞模型，首次给出了磁逆多光子非线性Compton散射的谱功率。     

离子原子碰撞过程中反冲离子飞行时间谱的蒙特卡罗模拟研究

基于蒙特卡罗方法,建立了程序模拟离子与原子碰撞中的反冲离子飞行时间谱.模拟入射离子束的空间密度分布,原子束密度的空间分布,靶原子的初速度分布, 根据反应几率产生不同电荷态反冲离子,并求出反冲离子飞行时间后,对每次模拟事件根据飞行时间进行累计,就得到反冲离子的飞行时间谱.模拟结果与实验(Ar12+-Ar) 测量到的TOF谱进行了分析比较,并进行了定性讨论     

轻基体中稀土氧化物的X射线荧光分析：非相干散射应用研究

本文通过研究轻元素的非相干散机机制，将非相干散射和特征线以散射归－化相结合计算表观浓度，利用强度校正模型和线性方程组的最小二乘法回归分析以及实验室标样，建立了轻基体之－Ｌｉ２ＣＯ３中少量Ｓｃ２Ｏ３，Ｙ２Ｏ３，Ｌａ２Ｏ３，Ｔｍ２Ｏ３和Ｌｕ２Ｏ３的Ｘ射线荧光分析方法，本方法测定的精密度均优于４．０％，最佳的可达２．１％。这种定时分析方法具有准确，简便，快速和多元素同时测定等优点。     

布里渊散射谱相干检测的消偏振衰落技术

在布里渊光时域反射计（BOTDR）的相干检测系统中,为减小偏振失配对布里渊谱测量精度的影响．针对后向布里渊散射光偏振态沿光纤随机变化,而同一记录点在重复采样周期内几乎不变的特点,结合偏振分集和扩展的思想,提出了实现简单而有效的时域偏振分集技术。理论分析表明,不管布里渊散射信号光的偏振态如何随机变化,采用该技术有较稳定的信号光功率与本振光被外差接收,接收信号对偏振态随机变化不敏感。系统实际上可基本不改变原系统体系,只对本振光施以无循环反馈的简单偏振控制。在布里渊时域反射计系统巾实验对比了采用与不采用该技术的结果,表明前者的接收信号功率幅度约是后者的四分之一．抑制幅度起伏效果明显。     

相干反斯托克斯拉曼散射显微镜的成像特性

对自身不发荧光且不便于荧光标记的化学或生物学样品，集相干反斯托克斯拉曼散射与激光共焦扫描显微镜于一身的相干反斯托克斯拉曼散射显微镜是一种好的选择。因为相干反斯托克斯拉曼散射是一种非线性过程，相干反斯托克斯拉曼散射显微镜的显微成像特性与一般的共焦显微镜非常不同。首先计算了焦点附近相干反斯托克斯拉曼散射激发场的偏振分布，然后，利用格林函数方法，得到了以赫兹偶极子为源的波动方程的精确解，发现对于不同的成像配置和样品形状，像场的相干反斯托克斯拉曼散射场分布非常不同，因此传统的显微镜成像表征方式（如点扩展函数）将不再能描述相干反斯托克斯拉曼散射显微镜的成像特性。     

爆炸物的X射线相干散射实验研究

采用同步辐射连续光谱的X射线(1.2-38.2KeV),对数种爆炸物(含铝黑色炸药、黑色炸药、黑索今、纯硝铵炸药、硝铵炸药和TNT)和非爆炸物(糖、奶粉、咖啡、纸等)进行了小角度的X射线散射实验,得到了上述几种爆炸物和非爆炸物的小角度相干散射谱. 从爆炸物的X射线散射谱中可以找到他们各自的特征衍射峰作为他们的"指纹",从而可以将爆炸物从非爆炸物中鉴别出来     

The collision frequency of electron-neutral-particle in weakly ionized plasmas with non-Maxwellian velocity distributions

The collision frequencies of electron-neutral-particle in weakly ionized complex plasmas with the non-Maxwellian velocity distributions are studied. The average collision frequencies of electron-neutral-particle in plasmas are accurately derived. We find that these collision frequencies are significantly dependent on the power-law spectral indices of non-Maxwellian distribution functions and so they are generally different from the collision frequencies in plasmas with a Maxwellian velocity distribution, which will affect the transport properties of the charged particles in plasmas. Numerically analyses are made to show the roles of the spectral indices in the average collision frequencies respectively.     

彩色图像的非相干光相关识别

提出一种用非相干光系统识别彩色图像的方法,将脸色图像分解成三个单色像处理,设计一可实现的仅相位光学传递函数,对其进行带能优化,人而提高信噪比并使相关峰锐化,通过一对滤波器来合成该光学传递函数,获得了采色图像相关识别的实验结果。     

Optimal Incoherent Filtering for Distortion-Invariant Image Recognition

An optimal incoherent filter is proposed for distortion-invariant correlation. The optical transfer function (OTF) of the correlator is specified as a realizable phase-only term which is optimized by the simulated annealing algorithm. The phase-only OTF is used in image recognition to produce a sharp peak response and can be generated by dual-filter synthesis. Image recognition is achieved by subtracting two spatially incoherent correlation outputs produced from a positive and negative filters with an input image. Computer simulations show that the proposed correlator can yield a sharp correlation peak with excellent distortion tolerance.Presented at 1996 International Topical Meeting on Optical Computing (OC ‘96), April 21–25, Sendai, Japan     

Complete spectrum of kinetic eigenmodes for plasma oscillations in a weakly collisional plasma

Kinetic eigenmodes of plasma oscillations in a weakly collisional plasma, described by a collision operator of the Fokker-Planck type, are obtained in closed form for initial-value as well as for boundary-value problems. These eigenmodes, which are smooth and compose a complete discrete spectrum, play the same role for weakly collisional plasmas as the Case-Van Kampen modes do for collisionless plasmas.     

Effect on Landau damping rates for a non-Maxwellian distribution function consisting of two electron populations

In many physical situations where a laser or electron beam passes through a dense plasma,hot low-density electron populations can be generated,resulting in a particle distribution function consisting of a dense cold population and a small hot population.Presence of such low-density electron distributions can alter the wave damping rate.A kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions.Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma.Strong damping is found for highly nonMaxwellian distributions as well as plasmas with a higher density and hot electron population.Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian.These results may be applied in both experimental and space physics regimes.     

非相干泵浦过程对光学双稳的影响

研究了低能级偶极子的非相干泵浦过程环形腔中双稳行为的影响，结果表明，耦合系统的双稳机制为非相干泵浦过程的干涉性，双稳迟滞环与非相干泵浦场有严格的对应关系，在一定条件下，甚至出现多稳态，可以利用非相干泵浦的干步性能控制光学双稳。     

X-ray spectra of high temperature tungsten plasma calculated with collisional radiative model

Tungsten is regarded as an important candidate of plasma facing material in international thermonuclear experimental reactor （ITER）, so the determination and modeling of spectra of tungsten plasma, especially the spectra at high temperature were intensely focused on recently. In this work, using the atomic structure code of Cowan, a collisional radiative model （CRM） based on the spin-orbit-split-arrays is developed. Based on this model, the charge state distribution of tungsten ions is determined and the soft X-ray spectra from high charged ions of tungsten at different temperatures are calculated. The results show that both the average ionization charge and line positions are well agreed with others calculations and measurements with discrepancies of less than 0.63% and 1.26%, respectively. The spectra at higher temperatures are also reported and the relationship between ion abundance and temperature is predicted in this work.     

Effect on Landau damping rates for non-Maxwellian distribution function consisting of two electron populations

In many physical situations where a laser or electron beam passes through a dense plasma, hot low-density electron populations can be generated, resulting in a particle distribution function consisting of a dense cold population and a small hot population. Presence of such low-density electron distributions can alter the wave damping rate. Kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions. Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma. Strong damping is found for highly non-Maxwellian distributions as well as plasmas with higher dense and hot electron population. Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian. These results may be applied in both experimental and space physics regimes.     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Observations of plasma line splitting in the ionospheric incoherent scatter spectrum

Wide-bandwidth ionospheric incoherent scatter (IS) spectra obtained using the Arecibo IS radar show the occurrence of a split in the plasma line (i.e., two plasma lines) when the plasma frequency is close to the second harmonic of the electron gyrofrequency. This split is predicted in the IS theory for a magnetized plasma, but observations have never been reported. Here we present the experimental results and theoretical calculations supporting the observations. These results may assist in understanding the behavior of Langmuir waves in the magnetized plasma and are a validation of what historically was a somewhat controversial aspect of the IS theory.