多模式光学数字全息实验教学系统

研究设计了一种多模式现代光学数字全息成像实验教学系统.该系统可通过多光路模式与CcD技术相结合建立并记录数字全息图频率场,采用不同数学算法和程序实现全息图的全数字化重构再现与图像的三维测量,并通过界面设计详细演示数字全息成像的原理与过程.     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

数字全息显微术中重建物场波前的相位校正

数字全息显微术克服了传统光学显微术无法直接提取样品相位信息的缺点,可以对活体细胞组织等相位型生物样品进行定量测量和有效观察。但在数字全息显微成像过程中,像场弯曲会对再现像相位分布的测量和观察产生影响。提出一种采用相位相减来校正数字全息再现像像场弯曲的方法。通过在样品加入前后两次拍摄全息图,并对数值重建像分别进行去包裹运算再令其相减,即可实现对像场弯曲的有效校正,对蝉翼和大蒜表皮细胞等相位型物体进行测量,并采用数值校正和相位相减两种方法对像场弯曲进行校正。与现有的数值校正方法相比,利用相位相减获得样品三维相位信息的方法更为简单、可靠,是校正像数字全息再现场弯曲的有效方法。     

Three-dimensional object recognition from digital Fresnel hologram by wavelet matched filtering

We propose and demonstrate a digital holographic technique for 3D object recognition and classification. One Fresnel digital hologram of each of the 3D objects to be classified is recorded. The electronic holograms are processed digitally to retrieve 3D object information as 2D digital complex images. We use this method to classify four physical objects in a 3D scene into two classes. Results are presented from an experiment to demonstrate the proof of the concept.     

Polarization phase shifting in digital holographic microscopy

In the present work we have made use of polarization phase shifting in digital holographic microscopy (DHM) for three dimensional phase profiling of transmissive and reflecting microscopic samples. The Mach–Zehnder arrangement with proper polarizing elements (polarizer-masked cube beam splitter, quarter wave plate and a linear polarizer) is used for recording the phase-shifted digital holograms. The suggested procedure is simple and accurate and obviates the need of piezo devices for phase shifting. The phase profile of the specimen is reconstructed from the holograms by using standard phase shifting algorithms.     

Color lensless digital holographic microscopy with micrometer resolution

Color digital lensless holographic microscopy with micrometer resolution is presented. Multiwavelength illumination of a biological sample and a posteriori color composition of the amplitude images individually reconstructed are used to obtain full-color representation of the microscopic specimen. To match the sizes of the reconstructed holograms for each wavelength, a reconstruction algorithm that allows for choosing the pixel size at the reconstruction plane independently of the wavelength and the reconstruction distance is used. The method is illustrated with experimental results.     

Automatic three-dimensional tracking of particles with high-numerical-aperture digital lensless holographic microscopy

We present an automatic procedure for 3D tracking of micrometer-sized particles with high-NA digital lensless holographic microscopy. The method uses a two-feature approach to search for the best focal planes and to distinguish particles from artifacts or other elements on the reconstructed stream of the holograms. A set of reconstructed images is axially projected onto a single image. From the projected image, the centers of mass of all the reconstructed elements are identified. Starting from the centers of mass, the morphology of the profile of the maximum intensity along the reconstruction direction allows for the distinguishing of particles from others elements. The method is tested with modeled holograms and applied to automatically track micrometer-sized bubbles in a sample of 4 mm3 of soda.     

粒子场数字全息诊断中的再现算法研究

 粒子场的数字全息诊断中,良好的再现算法能够在较短的时间内给出高质量的再现像。利用标准粒子板模拟单层面的粒子场,使用大面阵CCD实现同轴数字全息记录,得到了大尺寸的数字全息图。针对4种数字全息再现算法,本文从再现图像的质量、再现全息图的大小和计算速度3个主要方面进行了比较研究,结果表明角谱算法(FFT-AS)具有再现图像背景均匀,再现结果中无物理图像压缩,可以再现大尺寸的全息图且具有较快计算速度的优点,适合于粒子场同轴数字全息图的再现计算。     

Wave front reconstruction of Fresnel off-axis holograms with compensation of aberrations by means of phase-shifting digital holography

Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calculating through the Fresnel–Kirchhoff integral. A phase-shifting Mach–Zehnder interferometer is used for recording four-quadrature phase-shifted off-axis holograms. The basic principle of this technique and its experimental verification are described. We show that the application of this algorithm allows for the suppression of the zero order of diffraction and of the twin image and that the contrast of the reconstructed images can be further enhanced by digital compensation of the aberrations introduced by the holographic recording system     

Wavelength-scanning digital interference holography for optical section imaging

We propose and experimentally demonstrate a simple digital holographic method that allows reconstruction of three-dimensional object images with a narrow depth of focus or axial resolution. A number of holograms are optically generated by use of different wavelengths spaced at regular intervals. The holograms are recorded on a digital camera and reconstructed numerically. Multiwavelength interference of the holograms results in images of the contour plane whose thickness can be made arbitrarily narrow. Objects at different distances from the hologram plane are imaged clearly and independently, with complete suppression of the out-of-focus images. The technique is available only in digital holography and should have useful applications in holographic microscopy.     

An error detection and recovery algorithm for the transmission of digital holography over noisy channels

Digitalization enables and expertise storage and transmission of holographic data. However, the reconstructed object image is vulnerable to transmission errors over the noisy channel. We present a novel algorithm of what we believe is the first approach to reduction of noise effects on digital holograms corrupted by transmission errors. To accomplish this work, we exploit new interdependencies on the interference holograms and develop a detection-based algorithm to detect error points and to identify the corresponding interference holograms with the largest errors. In the reconstruction process, the conventional four-step algorithm is used for the recovery of error-free points. In contrast, a three-step algorithm is employed to reconstruct error points by removing the largest error holograms. With accurate detection, the proposed algorithm is capable of recovering the object image from digital holograms with severe transmission errors. It is shown that the proposed algorithm provides much better reconstruction performances than the conventional four-step reconstruction algorithm in an error-prone environment.     

空间光调制器曲面拼接实现全息三维显示视角拓展

本文对多空间光调制器不同拼接方式拓展全息三维再现像视角的方法进行了分析,基于多片空间光调制器拼接拓展视角的思想,利用平面反射镜、分光镜和两片透射式空间光调制器设计了曲面拼接系统,进行了全息三维再现像的视角拓展实验研究。用该系统对四棱锥物体的层析菲涅尔衍射全息图进行再现,结果表明,总视角由基于单片空间光调制器的1.7°增大到3.2°,即拓展到约1.9倍,分光镜能够消除两片空间光调制器间的间隙,实现无缝拼接。该方法同样适用于更多空间光调制器的曲面拼接中,可以有效地拓展全息再现像的视场角大小。     

基于DMD的数字全息显示及其再现像质增强

采用DMD作为空间光调制器构建了一套数字全息显示系统.分析了数字全息图光学再现中影响再现图像质量的因素,提出了一种采用频域滤波重建高条纹对比度滤波全息图来改善其光学再现图像质量的新方法.采用信噪比及图像亮度作为评价参量,对原始全息图和滤波全息图的数值再现像进行定量分析表明,滤波后全息图的再现像质量明显优于原始全息图的再现像.基于DMD数字全息显示系统的光学再现实验也验证了理论分析结果.     

Holographic imaging with a nanometer resolution using compact table-top EUV laser

Holographic 2D/3D imaging with nanometer resolution using short wavelength extreme ultraviolet (EUV) light is presented in this paper. Gabor’s holograms were recorded with a highly coherent table top EUV laser with different numerical apertures demonstrating ultimately a spatial resolution of 46+/−2 nm, comparable with the illumination wavelength, in 2D holographic imaging. Three dimensional images were obtained from a single high numerical aperture hologram recorded in a high resolution photoresist and numerically reconstructed at different image planes, allowing numerical optical sectioning with a lateral resolution ∼170 nm and depth resolution of 2.4 μm. The holograms were recorded in a high resolution photoresist and digitized with an atomic force microscope. To assess the spatial resolution of the numerical reconstructions of the holograms a correlation method was used. The algorithm allows for simultaneous estimation of the resolution and the feature size of the image under analysis.     

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.     

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.     

Real-time spatiotemporal division multiplexing electroholography for 1,200,000 object points using multiple-graphics processing unit cluster

Computationally, the calculation of computer-generated holograms is extremely expensive, and the image quality deteriorates when reconstructing three-dimensional(3 D) holographic video from a point-cloud model comprising a huge number of object points. To solve these problems, we implement herein a spatiotemporal division multiplexing method on a cluster system with 13 GPUs connected by a gigabit Ethernet network.A performance evaluation indicates that the proposed method can realize a real-time holographic video of a3 D object comprising ~1,200,000 object points. These results demonstrate a clear 3 D holographic video at32.7 frames per second reconstructed from a 3 D object comprising 1,064,462 object points.     

Securing complex and multi-plane data in a lens-less digital holographic information system that uses position-phase-shifting geometry

A digital holographic information system can process complex three-dimensional (3-D) object information. We demonstrate a scheme for securing complex and 3-D information in the context of in-line digital holography. Double random phase encoding in the free-space propagation domain of light is used to secure the complex information. Encrypted in-line digital holograms are recorded using the position-phase-shifting method. The encrypted complex image at the CCD recording plane is retrieved from the real-valued digital holograms, and is used for decryption. The robustness of the method has also been studied for various securing keys used in the method against blind decryption. A layer-by-layer information retrieval from the encrypted digital hologram is also discussed. The method can also be used to secure digital complex information in a virtual optics modality using holographic principles.     

A novel three-dimensional holographic display system based on LC-R2500 spatial light modulator

A novel holographic display system is proposed in this paper. The system takes LC-R2500, a kind of reflective liquid crystal spatial light modulator, (LC-SLM) as the core display unit, which can meet the requirement of real-time reconstruction of three-dimensional (3D) objects from holograms in free space. The relationship between hologram recording and image reconstruction is discussed, and the parameters associated with the magnification of reconstructed image over original object are determined. Experimental results of holographic display using the system are also given in the end.