基于图像处理的条纹相机扫描非线性修正

为了使条纹相机输出图像达到更高的测量准确度,提出一种基于图像处理的扫描非线性修正算法. 该算法根据给出的标称扫描速度拟合出扫描速度曲线,求出每道的扫描速度,取其算术平均值作为一个标准,根据每道的扫描速度与该标准的大小关系来修正像素的位置和亮度. 实验结果表明,可以将测量非线性由原来的8%减小到2%以下.     

条纹相机非线性修正算法

 条纹相机扫描电路的非线性会导致条纹图像时间与强度信息的失真。为了使条纹相机输出图像更加接近实际目标从而得到更高的测量精度,提出一种扫描非线性修正算法。该算法根据给出的标称扫描时间拟合出扫描时间曲线,求出每道的扫描时间,取其算术平均值作为一个标准,根据每道的扫描时间与该标准的数值大小关系来求出每个像素的修正系数,取图像与该系数矩阵的乘积即可完成图像的位置和灰度的修正。实验结果表明可以将测量非线性由原来的8% 减小到2% 以下。     

用于双光子激发荧光寿命显微成像的高重复频率皮秒扫描相机

建立了一台基于新研制的高重复频率皮秒扫描相机的双光子激发荧光寿命显微成像系统,重点介绍所研制的高重复频率皮秒扫描相机。为了在高时间分辨力的同时扩大时间测量范围,实现大面积两维空间高时间分辨取样测量,从而提高采样速率和更有效地发挥扫描相机的作用,设计和研制了一种大面积、高时间分辨力扫描变像管和一种重复频率高达1MHz的斜坡电压扫描电路。基于上述关键部件所研制的扫描相机具有重复频率高、扫描速度可调、时间分辨力高、工作面积大、非线性低、触发晃动小等优点。用钛宝石飞秒激光器作为激光脉冲源,通过脉冲提取器将76MHz的高重复频率降低为1MHz,采用可调延时器和标准具对扫描相机的时间分辨力、扫描速度和非线性进行标定。该系统的时间分辨力达到6.5ps,非线性为2.60%,可测量的时间范围从十几皮秒到几十纳秒。测量了若丹明6G和香豆素314两种标准荧光染料的荧光寿命,取得了与参考文献一致的实验结果。     

单模光纤共焦扫描显微系统研究

本文探讨一种使用单模光纤同时作为点源与点探测器的激光共焦扫描显微系统。该系统具有与传统共焦扫描相同的功能，但更容易操作，结构更简单，系统更稳定，文中给出系统的原理设计方案，并对其光学特性进行分析。     

自干涉合成孔径激光三维成像雷达原理

在直视合成孔径激光成像雷达(SAL)的基础上,提出了一种自干涉的产生三维成像的原理方法。首先对于交轨向正扫描和反扫描的柱面镜进行位置偏置,造成交轨向成像频谱的平移并产生相对线性相延,然后逐一对一对交轨向正扫描和反扫描收集聚焦像进行相干叠加,并由此产生自干涉。自干涉产生的交轨向平展条纹对于目标面的倾斜投射即可产生包含目标高度信息的波痕干涉图,最后通过解包裹算法产生表征目标表面轮廓的等位线图。本方法采用一发一收的雷达结构通过单航过干涉法实现三维成像,结构简单,原理有效,同时具有抗大气、运动平台等相位干扰能力。     

连续扫描全画素CCD摄像系统

本文阐述了连续扫描和隔行扫描ＣＣＤ（ｃｈａｒｇｅ－ｃｏｕｐｌｅｄｄｅｖｉｃｅ）摄像机的工作方式和特征，较详细地介绍了连续扫描ＣＣＤ的工作原理，用图示给出了两种扫描方式的比较。连续扫描方式可从每一个独立像素中获得在一个信号曝光周期之间产生的信号。对于在高分辨率成像情况下，在必需捕捉迅速运动目标的应用领域中，连续扫描ＣＣＤ是最佳的选择。     

基于衍射模型的Z扫描理论

以菲涅耳－基尔霍夫衍射理论为基础，建立了非线性光学介质对高斯光束的衍射模型，从一种新的角度解释了Z扫描现象，这种理论不仅在小非线性相移的情况下与传播Z扫描理论的结果完全一致，而且还适用于大非线性相移的情况。数值计算表明，随着非线性相移的增大，原来近似对称的Z扫描曲线发生畸变，谷的透过率被饱和抑制而峰的透过率被增强。通过开孔的光功率随着入射激光功率的增加会出现振荡衰减现象。     

激光在雾中传输的衰减研究

根据雾滴的尺寸分布模型及辐射雾和平流雾含水量与能见度的经验关系,运用Mie理论及其Van de Hulst近似计算了衰减效率因子, 并结合Deirmendjian对其进行修正,详细分析了激光在雾中的衰减计算公式。 在考虑前向散射时进一步结合Adarsh Deepak和O.H.Vanghan提出的前向修正系数, 得出前向散射修正后的衰减公式, 分析了雾的前向散射对激光传输的影响。 最后将修正后的衰减与常用经验衰减模式相比较, 表明前向散射修正后雾对激光的衰减更加接近实际工程应用。     

测量光折变非线性参量动态行为的一种新方法

在z扫描方法的基础上，提出了一种测量光折变非线性参量动态行为的新方法——时间扫描方法.理论和实验研究结果表明，这种新方法是精确、可行的. 关键词： 时间扫描方法 z扫描方法 非线性折射率 非线性吸收     

基于激光半主动的弹道修正系统修正能力的研究

弹道修正技术是为了解决射程与精度的矛盾而采用的一种有效方法。激光半主动弹道修正是采用激光半主动检测落点误差,通过对鸭舵进行弹道修正来提高打击精度的。分析了激光半主动弹道修正系统的工作原理和尾翼式微旋火箭弹鸭舵执行机构控制力,建立了尾翼式微旋火箭弹的刚体弹道,在最大周期平均控制力下持续对由弹道修正的弹道修正能力进行了仿真,得到不同启控时间的弹道修正能力。为激光目标指示器、探测器、鸭舵执行机构协调设计提供了理论依据。     

高能激光束在线测量系统的光强衰减设计

 针对环形光刀取样式高能激光束在线测量系统应用中光电探测器线性饱和功率密度低而被测高能激光功率密度高的特点,采用对取样激光扩束和介质膜衰减片级联衰减的方式,实现了数千倍的线性光强衰减。介绍了环形光刀扫描取样及其扩束衰减原理,并对介质膜衰减片在激光入射角 0°~15° 和功率密度1~1 000 W/cm²条件下的透过率特性进行了分析,用实验验证了该光强衰减设计的有效性。     

Nonlinear unbalanced Bessel beams in the collapse of Gaussian beams arrested by nonlinear losses

Collapse of a Gaussian beam in self-focusing Kerr media arrested by nonlinear losses may lead to the spontaneous formation of a quasi-stationary nonlinear unbalanced Bessel beam with finite energy, which can propagate without significant distortion over tens of diffraction lengths, and without peak intensity attenuation while the beam power is drastically diminishing.     

A simple model of ultrasound propagation in a cavitating liquid. Part I: Theory, nonlinear attenuation and traveling wave generation

The bubbles involved in sonochemistry and other applications of cavitation oscillate inertially. A correct estimation of the wave attenuation in such bubbly media requires a realistic estimation of the power dissipated by the oscillation of each bubble, by thermal diffusion in the gas and viscous friction in the liquid. Both quantities and calculated numerically for a single inertial bubble driven at 20 kHz, and are found to be several orders of magnitude larger than the linear prediction. Viscous dissipation is found to be the predominant cause of energy loss for bubbles small enough. Then, the classical nonlinear Caflish equations describing the propagation of acoustic waves in a bubbly liquid are recast and simplified conveniently. The main harmonic part of the sound field is found to fulfill a nonlinear Helmholtz equation, where the imaginary part of the squared wave number is directly correlated with the energy lost by a single bubble. For low acoustic driving, linear theory is recovered, but for larger drivings, namely above the Blake threshold, the attenuation coefficient is found to be more than 3 orders of magnitude larger then the linear prediction. A huge attenuation of the wave is thus expected in regions where inertial bubbles are present, which is confirmed by numerical simulations of the nonlinear Helmholtz equation in a 1D standing wave configuration. The expected strong attenuation is not only observed but furthermore, the examination of the phase between the pressure field and its gradient clearly demonstrates that a traveling wave appears in the medium.     

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应用多光子非线性Compton散射模型,研究了Compton散射对等离子体中激光衰减特性的影响.提出了Compton散射是影响激光衰减的一个重要机制,给出了激光能量和功率衰减值的表达式,并进行了数值模拟.结果表明,Compton散射对等离子体中传输的激光能量和功率衰减值有较大影响,理论计算和数值模拟符合得很好.这也为判断等离子体中发生Compton散射提供了依据.     

Sound propagation in saturated gas-vapor-droplet suspensions with droplet evaporation and nonlinear relaxation

The Sound attenuation and dispersion in saturated gas-vapor-droplet mixture in the presence of evaporation has been investigated theoretically. The theory is based on an extension of the work of Davidson [J. Atmos. Sci. 32(11), 2201-2205 (1975)] to accommodate the effects of nonlinear particle relaxation processes of mass, momentum and energy transfer on sound attenuation and dispersion. The results indicate the existence of a spectral broadening effect in the attenuation coefficient (scaled with respect to the peak value) with a decrease in droplet mass concentration. It is further shown that for large values of the droplet concentration the scaled attenuation coefficient is characterized by a universal spectrum independent of droplet mass concentration.     

Compton散射下强激光等离子体空气冲击波波前的传输特性

 根据球对称激光等离子体空气冲击波在自由空间中传输的约束条件，对多光子非线性Compton散射的强激光等离子体空气冲击波波前的传输特性进行了研究，给出了散射下空气冲击波波前的运动方程，并进行了数值模拟。结果表明：该冲击波的衰减过程不仅与爆炸源和爆炸过程的特性、释放总能量、空气的弹性有关，而且还与散射有关，散射效应使冲击波的初始半径增大，衰减过程加快，能量转移率提高；数值模拟与实验结果符合得很好。     

The use of a hybrid model to compute the nonlinear acoustic performance of silencers for the finite amplitude acoustic wave

In the present study, a hybrid method is proposed for predicting the acoustic performance of a silencer for a nonlinear wave. This method is developed by combining two models: (i) a frequency-domain model for the computation of sound attenuation due to a silencer in a linear regime and (ii) a wavenumber space model for the prediction of the nonlinear time-evolution of finite amplitudes of the acoustic wave in a uniform duct of the same length as the silencer. The present method is proposed under the observation that the physical process of the nonlinear sound attenuation phenomenon of a silencer may be decoupled into two distinct mechanisms: (a) a linear acoustic energy loss that owes to the mismatch in the acoustic impedance between reactive elements and/or the sound absorption of acoustic liners in a silencer; (b) a nonlinear acoustic energy loss that is due to the energy-cascade phenomenon that arises from the nonlinear interaction between components of different frequencies. To establish the validity of the present model for predicting the acoustic performance of silencers, two model problems are considered. First, the performance of simple expansion mufflers with nonlinear incident waves has been predicted. Second, proposed method is applied for computing nonlinear acoustic wave propagation in the NASA Langley impedance duct configuration with ceramic tubular liner (CT57). Both results obtained from the hybrid models are compared with those from computational aero-acoustic techniques in a time-space domain that utilize a high-order finite-difference method. Through these comparisons, it is shown that there are good agreements between the two predictions. The main advantage of the present method is that it can effectively compute the nonlinear acoustic performance of silencers in nonlinear regimes without time-space domain calculations that generally entail a greater computational burden.     

材料非线性衰减系数的二次谐波测量方法研究

采用有限幅值法测量材料在基波和非线性引起的二次谐波作用下的衰减系数:利用准线性下的KZK方程推导基波和二次谐波的声压分布,并提取波束修正系数;采用短纯音信号进行非线性实验,对检测得到的基波和二次谐波声压进行衍射修正处理,有效抑制衍射对衰减系数测量的不利影响,继而通过线性拟合的方法计算得到更精确的基波和二次谐波的衰减系数。以水为例进行实验,研究了实验测量所得衰减系数的频率依赖关系,结果表明在非线性条件下水的衰减系数与频率间存在较强的线性关系,而线性条件下衰减系数随频率呈现二次方增长的特性则不适用于非线性条件。该研究提出了准确测量非线性声波衰减系数的方法,为更有效地应用非线性超声检测提供理论依据。      

垂直载荷下湿玻璃珠样品的声速和衰减测量及非线性声学响应

为了分析垂直载荷下颗粒物质的声速、声衰减系数、谐波非线性等特性,本工作采用飞行时间法测量了不同含水量下声速随压强的变化规律,并利用傅里叶变换法分析了干、湿玻璃珠样品的声衰减和非线性声学特性。结果表明:干、湿玻璃珠样品中的声速、声衰减系数以及谐波非线性均随压强呈幂律变化;湿颗粒样品中随着液体含量增多,声速逐渐增加,超声波透过湿颗粒样品时的能量耗散和非线性逐渐减小。分析原因表明,压强和孔隙流体改变了颗粒之间的接触分布,使得颗粒体系的声速、声衰减以及谐波非线性等特性都随之发生变化。     

Visualization of human umbilical vein endothelial cells by acoustic microscopy

The morphology and acoustic properties of the human umbilical vein endothelial cells (HUVECs) were evaluated using a scanning acoustic microscope system. HUVECs were cultured for 4 days and exposed to the endotoxin for 4 h. The frequency of the scanning acoustic microscope was variable between 100 and 210 MHz. By changing the measuring frequency, ultrasonic amplitude and phase were measured and the quantitative value of attenuation was calculated. Before and after endotoxin stimuli, HUVECs were observed by scanning acoustic microscopy and the attenuation was measured. The acoustic images were successfully obtained to identify the outer shape of the HUVEC and the location of the nucleus in the cell. The attenuation of the nucleus is higher than that of the cytoplasm. The attenuation of the cytoplasm was increased and became inhomogeneous after endotoxin exposure. This finding would be related to the change of F-actin filaments, which is the main component of the cytoskeleton. Scanning acoustic microscopy is useful for assessing the cellular viscoelastic properties since it can detect both the morphological and acoustic changes without contacting the cellular surface.