Variable Phasenkontrast-Anordnungen zur Messung der absoluten Lichtphase

Normally, in phase contrast microscopy, a non-periodic object in the object plane is to be studied, and the phase strip in the pupil plane has to be known. But in these new phase measuring methodes, a known periodic object (a phase grating, particularly) in the object plane produces adiscrete spectre in the pupil plane the zeroth and higher orders of which can easily be influenced independently. This is done by the unknown phase object acting as the phase strip in the pupil plane. The influence of the strip on the final image is compensated by adjusting a second, variable, phase strip, or by superimposing a variable amount of dark-field image to give zero contrast in the final image. Phase and amplitude of the unknown object can then be calculated from the half-shadow setting parameters.     

Full field deformation measurement of centimeter sized objects using optical phase retrieval

Most papers in the field of optical phase retrieval either consider only the intensity (or amplitude) profile of the object under inspection (or scatterer location in the X-ray version), or a uniform tilt/rotation of the object beam. However, phase retrieval is able to recover the phase profile of the object (beam) as well, which theoretically makes the observable interference of phase retrieved object waves possible. In this paper we demonstrate this principle experimentally on centimeter sized deformable reflective objects (as large as 40 mm by 40 mm) and corresponding simulations are also presented. When the CCD camera is moved along the optical axis in the Fresnel region, the interference fringes of the displacement field have low contrast. On the other hand, when an imaging setup is built, and the camera moves near the image plane, high fringe contrast can be obtained. These fringes however suffer from some phase error. In our work the iterative modulus projection algorithm was used as a simply implementable phase retrieval method.     

Digital ultrasonic speckle phase-shifting method

The digital ultrasonic speckle phase-shifting method (USPM), which is introduced in this paper, can be applied to the measurement of small displacement that is smaller than speckle size at the test point compared to traditional ultrasonic speckle correlation method (USCM). Using USPM, a digital ultrasonic reference signal is introduced to interfere with the ultrasonic speckle signal, which is picked up at the test point on an object surface and is referred to as the object signal. As the phase of the reference signal is shifted several times using the software and then they superimpose with the object signal respectively, the phase of the object signal can be calculated according to the intensities of the superimposed signals. If the object surface moves a small distance, the phase variation of the object speckle can be detected by the same process. As a result, the displacement of the object surface can be measured. Based on the feature of ultrasonic speckles, inner surface displacement of an object can be measured using this proposed method. In this case, the effect of outer surface roughness to the measurement accuracy of USPM is examined experimentally. The experimental results show that the measurement is successful when the displacement is smaller than half of the speckle size at the test point and the roughness parameter R_a of the outer surface of the specimen is less than about 5.47 μm.     

双随机相位编码光学加密系统的唯密文攻击

针对双随机相位编码光学加密系统的安全性分析表明，该系统属于线性对称分组密码系统，其线性性质为安全性留下极大隐患.在唯密文攻击下，仅根据密文估计出物面波函数的“支撑”(support)，然后利用迭代相位恢复算法获得物面波函数(其振幅是明文信息)，再根据物面波函数与频域密文的关系可推导出频谱平面的解密密钥.由于估计出来的物面波函数的“支撑”相对于真实的物面波函数的“支撑”有一定的平移，使得恢复的物面波函数与真实的物面波函数之间无论在振幅上还是相位上都存在平移，导致用推导出来的解密密钥去解密其他密文时所获得的明文与原始明文之间存在明显平移.然而，可依照这一先验信息，将估计出来的物面波函数的“支撑”在物面内遍历，从而找到逼近真实解密密钥的解.利用此解密密钥去解密其他密文时获得更好的解密效果. 关键词： 光学信息安全 双随机相位编码 唯密文攻击 函数支撑     

相位物体的相位检测分析方法

介绍了相位物体的相位检测方法,包括传统的暗场法、纹影法和相衬法,重点介绍基于图像处理的相位物体的双点源光束干涉测量与扫描成像方法,并比较它们的优缺点,同时对目前的研究进展进行了综述.     

Object plane detection and phase-amplitude imaging based on transport of intensity equation

By using transport of intensity equation (TIE), phase distribution of an object is retrieved from through-focus intensity images. This technique allows simple and robust phase imaging compared with an interferometric approach. However, it is hard to measure phase distribution when a dynamic object moves in the direction of an optical axis. To clear this problem, autofocusing TIE which is based on local statistics is proposed. The proposed technique achieves the detection of the object plane and the retrieval of a focused object phase distribution simultaneously. In this approach, an object plane is determined by the focusing techniques based on local statistics such as variance, gradient, and Laplacian of amplitude distribution, after phase distribution in an image sensor plane is retrieved by the TIE. The performance of these three statistics is evaluated in numerical and optical experiments, and a suitable focus value is determined for precise phase imaging.     

A new method of three-dimensional measurement by differential interference contrast microscope

Based on weak phase approximation and the partial coherence theory, we analyze the image characteristics of a phase object using a microscope. We show that the image of the phase object is formed by the interplay between the phase distribution and the defocus.Using this theory, we also show the image characteristics of a differential interference contrast (DIC) microscope.We develop a method for extracting the phase component from the DIC image using two images with different retardation to reconstruct the phase distribution of the object. We call our new microscope a “retardation-modulated DIC (RM-DIC) microscope”. We describe the RM-DIC microscope and confirm our method using grating samples with depths of 20 and 50 nm.To measure the three-dimensional (3D) figures of the microstructures on the object using a DIC microscope we need to extract the phase component from the DIC image and to deconvolute the phase component by means of the modulation transfer function (MTF) of the DIC microscope.We conclude that our RM-DIC microscope can take quantitative measurements of the phase distribution, making it a very useful tool for 3D measurement of an object’s microstructures.     

Surface profile measurement of moving objects by using an improved π phase-shifting Fourier transform profilometry

The π phase-shifting Fourier transform technique is introduced into the surface profile measurement of moving objects. A digital grating comprising two regions, which have a π phase shifting is projected onto the object. Two line-scan CCD cameras are used to capture two deformed fringe patterns with π phase shifting at the same time. As the object is moving, each point at the object surface can be captured twice. The digital correlation method is used to calibrate the experimental system. The zero-order component can be eliminated by subtracting intensities of the same surface point in two captured images. And then the phase can be extracted by Fourier transform without the disturbance of zero-order component. Experimental results demonstrate that this method is feasible for the moving surface profile detection and the measurable slope of height variation can be extended.     

Semiderivative real filter for microoptical elements quality control

The article presents a proposal for a new method of automatic quality control of microlenses arrays, which is based on a semiderivative real filter. The use of the semiderivative filter for examining pure-phase objects involves modifying the spatial frequency. The basis of the proposed setup is a 4f correlator setup with coherent light. The phase object examined is placed in the input plane of the correlator. Next, the light passes through a filter located in the frequency plane, which gives an intensity signal. In the output plane a charge-coupled device (CCD) camera registers the light intensity, the range of which informs the shape of the phase object. The proposed method is shift invariant, so it allows for examination of single elements or a set of micro-optical elements simultaneously. Additionally, the same setup allows for measuring the phase of objects whose thickness is either considerably smaller or much bigger than 2π.     

Interferometric microimaging based on geometrical spin-redirection phase

A novel scheme for an interferometric microscope with which to visualize a geometrical spin-redirection phase image that represents the local inclination of microsurface structures of an object is proposed. The observed phase depends on the state of polarization and the optical constants of the object material, which enable one to distinguish the spin-redirection phase from the conventional dynamical-phase. A preliminary experiment was performed, and the phase images obtained were found to be consistent with those predicted by computer simulation based on a theoretical model.     

Surface contouring by phase-shifting real-time holography using photorefractive sillenite crystals

This work proposes to obtain surface contouring by phase-shifting real-time holography using photorefractive sillenite crystals which provides the surface contouring from a change in phase of wavefront of the object illumination beam. The real-time holography using the photorefractive Bi₁₂SiO₂₀ crystal and the four-frame phase-shifting technique was used to obtain the phase map, this map was filtered by an anisotropic sin/cos filter and the unwrapping process used was the cellular-automata technique. We obtained experimental results of the surfaces of the large objects with real discontinuities, and these results agree with the dimensions of the object.     

Shifted-phase calibration for a 3-D shape measurement system based on orthogonal composite grating projection

This paper proposes a novel method for reducing measurement error caused by spectrum overlapping in orthogonal-composite-grating-based 3-D measurement method. For 3-D measurement systems based on orthogonal composite grating projection, spectrum overlapping causes phase of each deformed phase-shifting fringe changed differently, which violates the principle that the shifted phases between adjacent deformed fringes must be equivalent to 2π/3, and therefore results in phase measurement error. The proposed shifted-phase calibration method is based on that phase variation of each deformed fringe is independent of height and reflectivity of the measured object. Three composite gratings are projected on the reference plane, and each carrier channel includes three phase-shifting gratings needed in phase measuring profilometry (PMP). Because the adjacent phase-shifting fringes demodulated from the same carrier channel have the phase difference of 2π/3, we can respectively calculate the reference plane's phases of three carrier channels by the phase algorithm of PMP method, and the shifted phases between them are obtained. When an object is measured, the shifted phases between deformed phase-shifting fringes can be calibrated. A new 3-D measurement mathematical model is set to reconstruct object. Our experiments prove that the proposed method can effectively restrain the effect of spectrum overlapping and improve measurement accuracy almost one times.     

Stokes参量数字全息法实现相位物体成像

为实现对相位物体的无损检测和成像,克服数字同轴全息相位物体成像技术在消除零级像和孪生像的干扰时存在的系列问题,提出一种基于Stokes参量的新的数字同轴全息技术。该方法区别于传统的利用干涉光场来记录原始像项的数字全息方法,通过测量物参光合成光束的Stokes参量来分别得到这两束光的振幅和相位差,从而准确、唯一地获得原始像项;再利用数字再现即可重构物光的振幅和相位信息。实验中对弱吸收的相位样品进行了测量,得到样品清晰的振幅和相位分布。结果表明,采用该方法对相位物体进行数字全息再现,可以克服传统同轴全息图中零级像和共轭像对相位物体信息的严重干扰,对于提取相位物体的振幅和相位信息是可行和有效的。     

Novel Ghost Imaging Method for a Pure Phase Object

We propose a novel ghost imaging scheme which is especially served to a pure phase object. A spatially incoherent beam is mixed with a coherent beam of the same frequency field by a beamsplitter. Then we perform the ghost imaging scheme using the mixed beam. Our theoretical result shows that this approach is capable of reconstructing a pure phase object in joint-intensity measurement. The visibility of the images is also analysed for two pure phase objects, an optical wedge and a phase grating.     

Sur la restitution du signe de la phase en interferometrie

Phase variations are transformed into intensity variations by means of interferometry. It is then possible to form a visible image of a pure phase object. But then information on the sign of the phase or the direction of surface relief is lost. Principles of a method for extracting only the imaginary part of the complex amplitude of the object, which is an odd function of the phase, are studied. From this it is possible to obtain the sign of the phase.     

Passive ranging and a three-dimensional imaging system through wavefront coding

A single-image passive ranging and three-dimensional(3 D) imaging system with chiral phase encoding was proposed in 2011 [Opt. Lett. 36, 115(2011)]. A new theoretical analysis of the system in space domain is presented in this paper. We deduce the analytic relationships between the object distance and the point spread function, and between the object distance and the encoded image, respectively. Both the point spread function and the processed spectrum of the encoded image have two spots, which will rotate with the variation of the object distance. Then the depth map is extracted from the encoded image and it can be used to set up 3 D images. The theoretical analysis is verified by a wavefront coding system with a chiral phase which is generated by a phase-only liquid-crystal spatial light modulator. The phase generated by the liquid-crystal spatial light modulator is more flexible than the fixed phase mask and can be adjusted in real time. It is especially suitable for observing the object with a large depth of field.     

Phase-unwrapping algorithm in the presence of discontinuities using a system with crossed grating

A new phase-unwrapping algorithm for the phase map containing discontinuities by the use of a system with crossed grating is described in this paper. A crossed grating is projected onto the object in the usual way, the deformed grating image acquired is Fourier transformed and the frequency spectra for the individual gratings are separated. Using both phase distributions which have different sensitivities, the correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of a three-dimensional object with height steps are presented.     

Holographic real-time imaging through a phase distorted medium

In this note we report on a new experiment using Fe-doped LiNbO₃ crystal (manufactured by ourselves) as a recording medium. It can compensate in real-time for the phase distorted wavefront of an object caused by a phase distorted medium (PDM). The wavefront of the object is required to pass through the PDM once only.     

Multicolor digital holography with an achromatic phase shifter

Multiwavelength recording and reconstruction of a three-dimensional object are realized by use of phase-shifting digital holography. Red, green, and blue lines emitted from a white-light He-Cd laser are used for one-step recording of the complex amplitude of the object with a color CCD camera, in which a phase shift is introduced with an achromatic phase shifter based on the geometric phase. Three color images are reconstructed and successfully combined in a computer by use of Fresnel transformation based on a convolution.     

Visualization of a Phase Object by Two-Wave Coupling in a Photorefractive Bismuth Silicon Oxide Crystal

We propose a method to visualize a phase object using a locally-controllable image amplification scheme we developed earlier which is based on two-wave coupling in a bismuth silicon oxide (Bi₁₂SiO₂₀, or BSO) crystal. In this method the BSO crystal is used as a phase plate in the configuration of Zernike’s phase contrast imaging system. The principle of the phase-visualization with two-wave coupling is presented. An experimental result to verify the proposed method is shown.