Apodization to produce a monotonically-decreasing,radially symmetrical,point-spread function

A class of apodized pupil functions is derived which have the property of producing a point-spread function which decreases monotonically with increasing radius. This in turn produces coherent line and edge images which are free of the usual subsidiary diffraction maxima and minima. An example of one of these functions is given, together with the point, coherent line and coherent edge images produced.     

Comparative analysis of the resolving power of optoelectronic imaging systems upon incoherent and coherent illumination of objects

Results of calculations of the resolving power (according to Foucault) of optoelectronic imaging systems with incoherent and coherent illumination under the conditions of atmospheric phase distortions are presented. It is suggested that incoherent optical images are formed in the case of incoherent illumination and speckle images are formed in the case of coherent illumination. The shape of objects observed is estimated from these images. The resolving powers are shown to be practically the same in the formation of incoherent optical images and speckle images in the case of strong phase distortions and smoothing of images by a matrix photodetector. At the same time, the limiting resolving power in the formation of incoherent optical images is twice as large as in the formation of speckle images.     

Objective evaluation of images reconstructed from digital in-line Fresnel holograms by using coherent background elimination

Quality of images reconstructed from in-line Fresnel holograms using elimination of a coherent background is quantitatively studied through computer simulation and experiment. The coherent background is digitally calculated by averaging an intensity of a recorded hologram. The results show that in spite of the fact that virtual image is still intact, the background elimination can resolve images with quality comparable to the phase-shifting technique.     

Detection and grading for esophageal varices in patients with chronic liver damage: comparison of gadolinium-enhanced and unenhanced steady-state coherent MR images

The purpose of this study was to compare observer interpreted steady-state coherent coronal images and gadolinium-enhanced axial images in terms of the detection and grading of esophageal varices. Magnetic resonance imaging (MRI) and gastrointestinal endoscopy were performed within 2 weeks in 90 patients with chronic liver damage, including 55 with untreated esophageal varices, for periodic screening purposes. Two blinded readers retrospectively reviewed T1- and T2-weighted images with gadolinium-enhanced (gadolinium image set) and steady-state coherent (coherent image set) images. Sensitivity for the detection of esophageal varices was higher (P<.001) in the gadolinium image set (76%) than in the coherent image set (35%); on the other hand, specificity was higher (P<.001) in the coherent image set (91%) than in the gadolinium image set (66%). Furthermore, area under the ROC curve was higher for the gadolinium image set (Az=0.823) than the coherent image set (Az=0.761) (P=.48). Moderate and weak positive correlations with endoscopic grades were found for the gadolinium image (r=0.48, P<.01) and coherent image sets (r=0.34, P=.018). The addition of steady-state coherent imaging to the current routine liver imaging protocol did not improve the detection or grading of esophageal varices, whereas gadolinium-enhanced imaging was found to be potentially valuable. Nevertheless, endoscopy was confirmed to be mandatory in patients with esophageal varices suspected by MRI of the liver.     

Coherent scattering phenomena in apertureless scanning near-field fluorescence microscopy

We study near-field fluorescence images of samples composed of aggregates of 100 nm dye-doped latex spheres. These images have been performed by a reflection Apertureless Scanning Near-field Optical Microscope (A-SNOM). We show that the near-field distribution in fluorescence A-SNOM images arises from coherent scattering phenomena between all spheres. This is a consequence of the coherent nature of the fluorescence emission of each single sphere. The results shown here are significant for all fluorescent samples characterised by a nonnegligible topography.     

Coherent optical generation of Hartley transform of real images

A new method to generate optical Hartley transform (OHT) for 2D real images is proposed. The method is based on polarization encoding of the coherent optical beam. Different coherent optical image processing techniques are discussed.     

Real-time joint spectral-spatial matched filtering

A technique for real-time joint spectral-spatial matched filtering is presented. The technique involves the real-time conversion of an input color image into a set of sampled monochromatic coherent images through the use of a tricolor grid and real-time spatial light modulator. These color-coded monochromatic images are then processed by a multi-channel, coherent matched filtering subsystem. The advantage of this technique over prior matched filtering methods is its ability to use both color and shape in recognizing objects.     

Optical filtering

This contribution deals with phase and amplitude filters used in coherent, partially coherent and incoherent illumination both for improvement of optical images and for detection of similarities (correlation). Other types of filters such as intensity filters, phase only filters etc. will be also discussed where appropriate. Most of the space, however, will be devoted to optical filtering in coherent illumination.     

彩色图象的光学信息处理

本文研究了在相干多色处理中用黑白透射介质进行彩色图象空间编码的方法。这个方法可应用于彩色象的信号检测、去模糊、及相加与相减。并且指出,类似于相干单色处理,这种多色处理方法有能力处理彩色图象。这个方法虽然有某些不足之处,例如需要对被处理对象事先进行编码。但是,这个方法展示了在彩色图象处理中的一个新的方向。而且,它并不只局限于处理彩色图象,也可应用于处理某些具有灰度变化的图象。 关键词：     

Fidelities of output coherent images produced by photorefractive two-wave mixing

We study theoretically the fidelities of output coherent images in incoherent-to-coherent conversion based on photorefractive two-wave mixing in the presence of an incoherent image-bearing beam. A vector version of the whole beam split step method is developed. The dependencies of the fidelities of output coherent images on geometric and physical parameters such as the incident direction of the beams, the intensity ratios between the beams, and coupling coefficients are investigated in detail. PACS 42.65.Hw     

Imaging of supersonic flow over a double elliptic surface

The coherent structures of flow over a double elliptic surface are experimentally investigated in a supersonic lownoise wind tunnel at Mach number 3 using nano-tracer planar laser scattering(NPLS)and particle image velocimetry(PIV)techniques.High spatiotemporal resolution images and velocity fields of both laminar and turbulent inflows over the test model are captured.Based on the time-correlation images,the spatial and temporal evolutionary characteristics of the coherent structures are investigated.The flow structures in the NPLS images are in good agreement with the velocity fluctuation fields by PIV.From statistically significant ensembles,spatial correlation analysis of both cases is performed to quantify the mean size and the orientation of coherent structures.The results indicate that the mean structure is elliptical in shape and the structural angles in the separated region of laminar inflow are slightly smaller than that of turbulent inflow.Moreover,the structural angles of both cases increase with their distance away from the wall.     

Digital microscopy using phase-shifting digital holography with two reference waves

A lensless, coherent optical microscope is described that uses a version of phase-shifting digital holography (PSDH) in conjunction with a field backpropagation algorithm to form coherent images of transmission-type objects. The PSDH is implemented by use of only two reference waves, in contrast with the usual implementation that requires four quadrature phase-shifting reference waves. Therefore only two digital holograms need to be recorded, and the complexity of the microscopic system is reduced. Experimental results are presented that compare images generated from conventional Gabor digital holography, two-reference-wave PSDH, and conventional white-light microscopy.     

小尺寸样品CARS图像信号分布实验研究

通过设计实验与分析模型,研究相干反斯托克斯拉曼散射成像对于样品尺寸小于系统点扩展函数尺寸的情况,分析相干反斯托克斯拉曼散射图像周围的depth的形成原因。分析过程首次引入轴向传输动态位移光线（此光线由相干体积元内轴心光线抽象出）对球形或柱形样品直径小于系统点扩展函数横向与轴向尺寸进行建模解析,对于所建模型定量分析结果表明,对于样品尺寸小于系统点扩展函数尺寸样品折射率调制了有效作用深度。Gouy相移只是其表观现象,是一个伴随性特征,因为物理学中存在的另一个极端,当样品尺寸足够小且具有相当的折射率,Gouy相移的作用近似为0,此时,样品周围的depth主要与样品的折射率及系统相干层析体积元内有效作用长度有关,相干反斯托克斯拉曼散射参量信号,具有自身的波矢匹配条件,不仅有大小,有方向,而且还受到样品自身材料折射率的影响比较明显。也就是对于参量过程波矢匹配条件是因,Gouy相移是伴随性特征。自此,通过相干反斯托克斯拉曼散射间接说明所用的紧聚焦参量信号成像过程,正是因为波矢匹配条件的存在使二次信号继承了激发光的紧聚焦特性,而拥有了继承性的Gouy相移,结合实验结果采用物理学的极端假设表明,Gouy相移不是产生depth的主要原因,主要原因是样品及周围的环境的折射率与系统相干层析体积元内有效作用长度之间共同作用的结果。而实验结果与模型定量分析的结果相吻合,此实验帮我们找到了影响CARS图像样品周围depth的成因机制,对于其他小尺寸样品的参量成像结果的分析具有一定的借鉴意义。通过设计实验,结合定量模型分析,首次明确造成小尺寸样品CARS图像周围的depth的真正原因,此抽象模型的拓展性对纳观参量过程的分析具有得天独厚的优势。抽象出的主能量光线动态位移模型成功分析纳观成像结果表明,相干作用长度之内有效作用长度及其行进路径的过程论的主因分析方法是研究纳观作用机制的最佳方法。     

非全息衍射投影（英文）

提出了一种无需全息计算和相干照明的衍射投影方法和投影系统,利用非相干的准直LED光源和傅里叶变换透镜取代全息迭代计算获得被投影图像的空间频谱,再利用空间频谱在自由空间中的瑞利索墨菲衍射实现了小投射比、无限景深的图像投影.详细推导了投影方法的成像过程,解析了投影系统的强度脉冲响应函数.实验搭建了一套非全息衍射投影系统,对投影过程中产生的像差和亮度不均匀进行矫正,获得了无相干噪音的高品质衍射图像,实现了投射比为0.87的无限景深的衍射投影.在相距大于800 mm的不同深度平面上同时获得了清晰的投影图像,从而验证了方法的可行性.该投影方法和系统在球幕投影、任意曲面屏幕投影和增强现实投影等领域具有潜在的应用.     

Speckle noise attenuation in optical coherence tomography by compounding images acquired at different positions of the sample

This study demonstrates a simple method for attenuating the speckle noise generated by coherent multiple-scattered photons in optical-coherence tomography images. The method could be included among the space-diversity techniques used for speckle reduction. It relies on displacing the sample along a weakly focused beam in the sample arm of the interferometer, acquiring a coherent image for each sample position and adding the individual images to form a compounded image. It is proven that the compounded image displays a reduction in the speckle noise generated by multiple scattered photons and an enhancement in the intensity signal caused by single-backscattered photons. To evaluate its potential biomedical applications, the method is used to investigate in vitro a caries lesion affecting the enamel layer of a wisdom tooth. Because of the uncorrelated nature of the speckle noise the compounded image provides a better mapping of the lesion compared to a single (coherent) image.     

部分相干同步辐射照射下光栅分数塔尔博特效应

基于高斯谢尔光束的相干模式分解理论和波动光学,建立了部分相干同步辐射硬X射线光束通过光学器件的传播模型。模拟了微聚焦X射线光束照射下光栅的分数塔尔博特效应,得到了聚焦光束的光强分布和相干特性变化,并分析了散焦光束入射下的光栅自成像。然后通过模拟准直光束入射下的光栅塔尔博特效应,得到了不同传播距离处自成像条纹的变化情况,分析了影响光栅自成像条纹形状的因素。通过光栅衍射条纹测量同步辐射相干度,发现对矩形相位光栅来说,应该对衍射图样进行傅里叶分解,求出各级傅里叶系数随传播距离的变化曲线,从而得到入射光束相干特性。     

Photorefractive two-wave mixing in the presence of an incoherent beam

We present the numerical results of the photorefractive two-wave mixing in the presence of an incoherent beam by considering the influence of the ratios of the intensities and the light-excitation cross sections of the incoherent beam to the coherent beams on the space-charge field and the effective coupling coefficient. The results show that the incoherent beam can control the intensity of the coherent beams effectively. The experimental results agree with the theory well. One application is demonstrated to obtain the positive and negative coherent replicas of an incoherent image. The coherent images have a resolution of 80.6 line pairs/mm. Received: 2 March 1999 / Revised version: 26 July 1999 / Published online: 20 October 1999     

基于旋转照明光的数字全息相干噪声抑制

提出一种数字全息相干噪声抑制方法。首先在照明光方位角给定的前提下,通过在极向平面内连续旋转照明光,实现在多角度照明条件下记录离轴数字全息图。然后对所获得的全息图分别重构,同时利用倾斜相差补偿算法和数字图像自相关配准方法分别补偿再现像的相位倾斜及横向偏移。最后将重构像进行非相干叠加,从而有效抑制再现像的相干噪声。实验结果及相关统计评价数据皆验证了该方法的有效性。     

Laser probing of biological tissues and the polarization selection of their images

Problems of increasing the signal-to-noise ratio in coherent images obtained in laser polarization probing of optically anisotropic architectonics of the morphological structure of biological tissues are discussed. Possibilities of polarization selection and contrast enhancement of such images screened by other biological tissues are analyzed.     

Synthetic phased-array terahertz imaging

We demonstrate terahertz (THz) imaging with enhanced spatial resolution by a synthetic phased array. A single mirror is used to separately form two different coherent, diffraction-limited THz images of the same point source. The two images are combined to yield a 4x resolution-enhanced image of the source in one dimension.