Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter

We present a digital holography microscopy technique based on a parallel-quadrature phase-shifting method. Two π/2 phase-shifted holograms are recorded simultaneously using polarization phase-shifting principle, slightly off-axis recording geometry, and two identical CCD sensors. The parallel phase-shifting is realized by combining circularly polarized object beam with a 45° degree polarized reference beam through a polarizing beam splitter. DC term is eliminated by subtracting the two holograms from each other and the object information is reconstructed after selecting the frequency spectrum of the real image. Both amplitude and phase object reconstruction results are presented. Simultaneous recording eliminates phase errors caused by mechanical vibrations and air turbulences. The slightly off-axis recording geometry with phase-shifting allows a much larger dimension of the spatial filter for reconstruction of the object information. This leads to better reconstruction capability than traditional off-axis holography.     

Surface Shape Measurement by Phase-Shifting Digital Holography

Surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed phase due to tilting of the object illumination. After phase-unwrapping it directly delivers surface shape. Its sensitivity depends on the tilting angle as well as on the initial incident angle. Although the sensitivity is the same as in the conventional fringe projection, a simpler setup is used without imaging lens and measurement depth is increased due to numerical focusing. We also performed noise suppression by employing nonlinear image-data compression technique that considers amplitude values and attained standard height deviation less than 30 #x03BC;m from a flat surface.     

Mapping of vibration amplitudes by time average holography in Bi12SiO20 crystals

We report the performance of a holographic set-up with a Bi₁₂SiO₂₀ (BSO) photorefractive crystal for measuring vibration amplitudes in a time average holography system. The volume hologram is recorded with the 514.5 nm wavelength of an Ar⁺ laser. In this set-up the reference beam is sinusoidally phase-modulated with the same frequency of the vibrating object. By increasing the value of the phase modulation, the fringes of the time average pattern run along the object surface, so that the vibration amplitude mapping is carried out. This technique allows the improvement of the measurement sensitivity compared with conventional time average holography, even for interferograms with poor visibility.     

Light-induced lens analysis in photorefractive crystals employing phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities of phase-shifting real-time holographic interferometry for the analysis of light-induced lens in photorefractive and nonlinear optical materials. We show that this technique can be used for quantitative evaluation of the phase distribution of a wavefront changed by a light-induced lens and, consequently, the refractive index changes in these materials. The basic principle of this technique combines real-time holographic interferometry with phase-shifting technique for interferogram analysis. This method is demonstrated with in situ visualization, monitoring and analysis in real-time and uses a Bi₁₂SiO₂₀ crystal as the holographic medium and a Bi₁₂TiO₂₀ as the test sample.     

Wave optics analysis by phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities in the phase-shifting real-time holographic interferometry using photorefractive crystals as the recording medium for wave-optics analysis in optical elements and non-linear optical materials. This technique was used for obtaining quantitative measurements from the phase distributions of the wave front of lens and lens systems along the propagation direction with in situ visualization, monitoring and analysis in real time.     

High-speed phase imaging by parallel phase-shifting digital holography

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second.     

Optical encryption of gray-level image using on-axis and 2-f digital holography with two-step phase-shifting method

In this paper we propose an encryption/decryption technique of gray-level image information using an on-axis 2-f digital holographic optical encrypting system with two-step phase-shifting method. This technique reduces the number of holograms in phase-shifting digital holography and minimizes the setup of the encryption system more than multistep phase-shifting technique. We are able to get the complete decrypted image by controlling the K-ratio which is defined as the reference beam intensity versus the object beam intensity. We remove the DC-term of the phase-shifting digital hologram to reconstruct and decrypt the original image information. Simulation results show that the proposed method can be used for encryption and decryption of a 256 gray-level image. Also, the result shows some errors of the decrypted image according to K-ratio.     

Real-time holographic interferometry using photorefractive sillenite crystals with phase-stepping technique

This work presents a holographic interferometer that uses the photorefractive sillenite crystals in diffusive regimen whose configuration exhibits diffraction anisotropy for real-time holographic interferometry. The writing–reading process of holographic interferogram was done in real-time, connected with an interferogram-analysis method that uses the phase-stepping technique for quantitative measurement of changes on an object. The holographic interferograms from the analyzed surface were captured and they were used to calculate the phase map with four-frame technique. The unwrapping process used was the cellular-automata technique. We obtained quantitative results for some applications: measurements of micro-rotation of surfaces, punctual micro-displacements on an aluminum plate, stress on a dog's jaw, among others; adding new promising applications possibilities for basic research, dentistry and technological areas.     

二阶总广义变分图像放大

提出了一种在相移数字全息中提取相移角的方法.该方法通过在相移数字全息中引入随机相位板对物光波的相位进行调制,使得物光波在全息面上的相位分布成为近似理想的随机分布,进而根据这种随机分布的统计性质对相移角进行提取.计算机模拟结果表明,该方法提取出的相移角与设定的相移角之间的相对误差小于千分之一.同时,经过对比采用随机相位板和不采用随机相位板的计算结果发现,物体衍射光波在全息面上的相位分布具有一定的相关性.     

Vibration Analysis by Phase Shifting Digital Holography

Phase-shifting digital holography has been used for the study of vibrating objects. The time-averaged complex amplitude of Fresnel diffracted field due to a vibrating object was obtained by using a three-step phase-shifting algorithm. Taking the inverse Fresnel transform of the complex amplitude resulted in an image of the object superimposed with Bessel fringes. The Bessel fringes are contour map of the vibration amplitude. By sinusoidally modulating the phase of the reference beam at the vibration frequency, the brightest fringe could be shifted to points of interest, thus extending the measurable range of vibration amplitude.     

Quantitative detection and compensation of phase-shifting error in two-step phase-shifting digital holography

Phase-shifting digital holographic technique is a powerful tool for the measurement of various physical parameters, such as object deformation and liquid or cell’s refractive index change. However, for an accurate measurement, phase-shifting error in the reference wave path is still a major issue. In this paper, three novel and simple algorithms are proposed to quantitatively detect and correct phase-shifting error for a pure phase object in two-step phase-shifting digital holography. Influence of phase-shifting error is illustrated, and the effectiveness of the proposed algorithms is demonstrated by numerical simulation results.     

Object recognition by use of polarimetric phase-shifting digital holography

Pattern recognition by use of polarimetric phase-shifting digital holography is presented. Using holography, the amplitude distribution and phase difference distribution between two orthogonal polarizations of three-dimensional (3D) or two-dimensional phase objects are obtained. This information contains both complex amplitude and polarimetric characteristics of the object, and it can be used for improving the discrimination capability of object recognition. Experimental results are presented to demonstrate the idea. To the best of our knowledge, this is the first report on 3D polarimetric recognition of objects using digital holography.     

Phase-conjugate wavefront generation via four wave mixing in Bi12GeO20 crystals - reflection hologram type

Phase-conjugate wavefront generation via real-time holography in degenerate four-wave mixing experiments in photorefractive crystals Bi₁₂GeO₂₀ is presented. The phase volume hologram responsible for the phase-conjugate wavefront generation is a reflection hologram. No external electric field is applied and electron diffusion is the main mechanism responsible for the formation of the hologram. The theoretical and experimental results for wavefront reflectivity as a function of the intensity ratio of the writing beams are given.     

MEMS微变形镜测试技术及算法研究

介绍了基于计算机控制的频闪显微干涉测量技术,实现了对MEMS微变形镜的表面形貌、离面变形、静态电压-位移曲线和谐振频率的测量。采用频闪成像、计算机微视觉技术以及基于最小二乘曲面拟合法的亚像素定位技术实现了对平面内微位移的测量;利用频闪成像以及5步相移干涉技术实现了对干涉相位的提取,建立了适合于MEMS微变形镜特性测试的相位解缠算法,恢复了代表被测物体表面形貌的真实相位,实现了微变形镜静动态特性的测试。测试结果表明:频闪显微相移干涉测量技术具有测量速度快、精度高、易实现自动控制等特点。     

一种在二步相移数字全息中实现准确相移的方法

相移数字全息中的相移准确性决定了重建结果的质量,本文提出了在二步相移数字全息中实现准确相移的方法.该方法使用数字电压源开环控制普通的压电陶瓷微位移器,通过连续以微小的间隔来改变施加在压电陶瓷微位移器上的电压,可以获得一系列对应于不同相移角的全息图像,进而可以利用这些全息图像重建出来物光波在全息面上的强度分布.实验中采用已被CCD直接记录的物光波在全息面上的强度分布作为标准来评价前面重建结果的质量,计算了这些重建结果和评价标准之间的相关系数,结果表明相关系数达到最大时对应的全息图具有准确的相移角π/2.实验中比较了使用所确定准确相移角和理论相移角分别重建出来物光波的质量,计算机模拟和实验的结果证实了该方法的有效性.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

Estimation of inner surface profile of a tube by two-wavelength phase-shifting digital holography

A novel phase-shifting digital holographic method for estimation of inner surface profiles of tubes is proposed. For surface contouring, a two-wavelength method using injection-current-induced wavelength changes of a laser diode is used. To obtain inner surface information on a tube, a cone-shaped mirror is set inside the tube. Speckle noise occurring in the reconstructed phase difference image is effectively suppressed by an adaptive filtering technique consisting of exponential averaging and masking filtering processes. Distribution of optical path length in the experimental alignment is calculated and well explains the experimental results. It is shown that the calculation of optical path length by a simple model can remove the distortion of profiles occurring in the experimental results and enable the estimation of the inner surface profile of an aluminum tube.     

Surface contouring by phase-shifting digital holography

Surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed object phases due to the tilt of object illumination. Surface height from a reference plane is directly obtained from the phase change. Its sensitivity depends on the tilt angle as well as on the initial incident angle. By proper selection of the angles we can derive surface height without phase unwrapping. The sensitivity can be enhanced by increasing the tilt angle. Then we need phase unwrapping that is sensitive to noise due to laser speckles in the reconstructed images. This noise could be suppressed by selecting phase values at points of the maximum product of amplitudes before and after the illumination change in the course of data reduction from 1024×1024 to 512×512 and by selecting paths for phase unwrapping by looking for the intensity maximum. The observed height resolution is 20 μm. Effects of numerical focusing have also been investigated. The present method has the same sensitivity as the fringe projection method, but it has larger measurement depth and is also applicable to the deformation measurement with the same arrangement.     

偏转平台剪切电子散斑干涉相移技术研究

在沃拉斯顿棱镜作为剪切器件的传统剪切散斑干涉术中,由于错位的二物光束同光路传播,很难通过将它们分开来引入附加相位的方法实现相移。本文提出的偏转平台法是利用平台上物体的偏转来引入附加相位的,从而可以实现剪切电子散斑干涉的相移。理论分析证明,物体的偏转可以引入稳定、线性的附加相位,并给出了物体偏转角度与附加相位之间的关系式;利用周边固定、中心加载圆盘进行了典型实验,给出了实验结果,证明偏转平台相移技术能够有效地从干涉条纹中提取位移导数信息。     

Hilbert reconstruction of phase-shifted second-harmonic holographic images

New techniques are presented that make phase-shifting holography viable for second-harmonic generation (SHG) holography with weak object fields. We developed an intrinsic phase shift calibration of SHG holograms, an algorithm that extracts the reference and object intensity directly from a set of phase-shifted holographic data, and a more robust phase-shifting holography reconstruction algorithm based on π-shifted hologram pairs that permits self-calibration of the phase shift and recovery of the complex field through a Hilbert transform.