Method of Increasing the Spatial Resolution in Digital Holographic Microscopy

A new method of increasing the spatial resolution in digital holographic microscopy is considered. The method is based on supplementing the initial hologram with results measured in the case of photodetector shifting in space by a value smaller than the resolution used. In contrast to other known approaches, this method does not require a system of equations to be solved.     

全息扫描镜直线扫描分析及像差校正

介绍了全息扫描镜的原理,给出了等空间频率分布及变空间频率分布的全息扫描镜结构.基于全息图相位及相位传递函数方法,分析了全息扫描镜产生直线扫描条件,推导出记录子全息图各参数之间的关系,得出了利用短波长光记录子全息图,用长波长光再现,实现线性扫描的结果.提出了由于波长移动引起的像差校正方法.分析了摆动与偏心对扫描特性的影响.简介了所设计的变空间频率分布的全息扫描镜.     

In-line holographic electron microscopy in the presence of external magnetic fields

It is now a well-known fact that the phase of electron waves is altered by external magnetic fields via the Aharonov-Bohm effect. This implies that any electron interference effects will be to some degree affected by the presence of such fields. In this study we examine the distortion effects of external (constant and variable) magnetic fields on electron interference and holography. For digital holography, the reconstruction of the object is done via numerical calculations and this leaves the door open for correcting phase distortions in the hologram reconstruction. We design and quantitatively assess such correction schemes, which decidedly depend on our knowledge of the magnetic field values in the holographic recording process. For constant fields of known value we are able to correct for magnetic distortions to a great extent. We find that variable fields are more destructive to the holographic process than constant fields. We define two criteria, related respectively to global and local contrast of the hologram to establish the maximum allowed external field which does not significantly hinder the accuracy of in-line holographic microscopy with electrons.     

数字全息三维显示关键技术与系统综述

三维全息显示能够表现出与真实物体一样的深度和视差,是一种理想的三维显示方法.但是,三维物体计算全息图计算复杂且计算量巨大,因此,如何快速生成三维物体计算全息图是数字三维全息动态显示中的关键问题之一.本文首先论述了数字全息三维显示的关键技术,包括物点散射法、体视全息法、层析法等三种三维物体计算全息图实现方法,一种RGB分离的真彩色全息显示实现方法和若干提高全息再现像质的方法;然后对几种最新典型的数字三维全息显示系统进行了技术分析;最后总结了数字全息三维显示领域的发展动态,指出三维全息显示技术会朝着实时、动态、更大尺寸、更高分辨率方向发展.     

Diabetes screening by telecentric digital holographic microscopy

Diabetes is currently the world's fastest growing chronic disease and it is caused by deficient production of insulin by the endocrine pancreas or by abnormal insulin action in peripheral tissues. This results in persistent hyperglycaemia that over time may produce chronic diabetic complications. Determination of glycated haemoglobin level is currently the gold standard method to evaluate and control sustained hyperglycaemia in diabetic people. This measurement is currently made by high‐performance liquid chromatography, which is a complex chemical process that requires the extraction of blood from the antecubital vein. To reduce the complexity of that measurement, we propose a fully‐optical technique that is based in the fact that there are changes in the optical properties of erythrocytes due to the presence of glucose‐derived adducts in the haemoglobin molecule. To evaluate these changes, we propose to perform quantitative phase maps of erythrocytes by using telecentric digital holographic microscopy. Our experiments show that telecentric digital holographic microscopy allows detecting, almost in real time and from a single drop of blood, significant differences between erythrocytes of diabetic patients and healthy patients. Besides, our phase measurements are well correlated with the values of glycated haemoglobin and the blood glucose values.     

Measuring metal plate vibrations by digital stroboscopic holographic interferometry of focused images

A method for digital stroboscopic holographic interferometry of focused images for measuring points of displacements of a metal plate vibrating at a resonant frequency is considered. Unlike classical holographic interferometry, in this method, the measurement process does not include the process of interferogram obtaining, recording, and interpretation.     

Digital in-line X-ray holography with zone plates

Single pulse imaging with radiation provided by free-electron laser sources is a promising approach towards X-ray microscopy, which is expected to provide high resolution images of biological samples unaffected by radiation damage. One fully coherent imaging technique for this purpose is digital in-line holography. Key to its successful application is the creation of X-ray point sources with high photon flux. In this study we applied zone plates to create such point sources with synchrotron radiation provided by the storage ring BESSY II. The obtained, divergent light cone is applied to holographic microscopy of biological objects such as critical point dried Navicula perminuta diatoms and human cells using photons with an energy of 250 eV. Compared to conventional experiments employing pinholes, exposure times are reduced by two orders of magnitude.     

Vacuum-ultraviolet Gabor holography with synchrotron radiation

We present the realization of high-resolution holographic microscopy using the original Gabor geometry and imaging with radiation in the vacuum-ultraviolet (VUV) spectral region. Synchrotron VUV radiation with a wavelength of 13.8 nm was focused on a small pinhole generating a highly divergent light cone suitable for digital in-line holography. Objects of different thickness and materials have been used to test the imaging properties of holographic microscopy in the VUV wavelength range. The effective numerical aperture was limited by the illuminated area of the detector, yielding a theoretical resolution below 1 microm and an experimental one of approximately 1 microm.     

Nano‐level position resolution for particle tracking in digital in‐line holographic microscopy

Three‐dimensional particle tracking in biological systems is a quickly growing field, many techniques have been developed providing tracking characters. Digital in‐line holographic microscopy is a valuable technique for particle tracking. However, the speckle noise, out‐of‐focus signals and twin image influenced the particle tracking. Here an adaptive noise reduction method based on bidimensional ensemble empirical mode decomposition is introduced into digital in‐line holographic microscopy. It can eliminate the speckle noise and background of the hologram adaptively. Combined with the three‐dimensional deconvolution approach in the reconstruction, the particle feature would be identified effectively. Tracking the fixed beads on the cover‐glass with piezoelectric stage through multiple holographic images demonstrate the tracking resolution, which approaches 2 nm in axial direction and 1 nm in transverse direction. This would facilitate the development and use in the biological area such as living cells and single‐molecule approaches.     

显微数字全息图相位的滤波法提取

显微数字全息的关键技术之一是其相位信息的提取。通过分析显微数字全息图的空间频谱特点,提出了一种新的相位提取方法。将数字全息图频谱进行搬移,使物光频谱中心移到频域坐标原点;设计有限脉冲响应(FIR)数字滤波器滤出物光频谱;求解滤波后信号的辐角得到全息图相位。对设计的实验系统进行了验证,实验结果表明采用提出的方法提取显微数字全息相位,完全可行,效果良好。     

Thin dynamic holograms with an asymmetric fringe profile

Results of an investigation and a comparison of schemes used for recording dynamic holographic gratings in a liquid-crystal spatial light modulator, which ensure grating profile asymmetrization and, thus, a significant increase in its diffraction efficiency, are presented. Three approaches are considered: digital, analog, and self-asymmetrization of the profile due to the effect of a secondary field induced in the nematic volume. It is demonstrated that the first two approaches provide recording of gratings with low spatial frequencies (several mm⁻1) and with an approximately equal rate of asymmetry (the potential efficiency of diffraction to the first order is 70–75%), while the third approach provides recording of gratings with a much higher spatial frequency (hundreds of mm⁻1), but with a lower efficiency (about 50%).     

Experiments and quantitative analysis of frequency division multiplexing confocal fluorescence microscopy with UV excitation

In this paper, we experimentally demonstrated a two-channel frequency division multiplexing confocal fluorescence microscopy system using a UV laser as the excitation source. In our two-channel frequency division multiplexing confocal fluorescence system, the incoming laser beam was divided into two beams and each beam was modulated with an individual carrier frequency. These two laser beams were then spatially combined with a small angle and focused into two diffraction-limited spots on the targeted cell (rat neural cell) surface to generate fluorescent signal. As a result, the fluorescent signals from two spots of the rat neural cell surface can be demodulated and distinguished during data processing. Furthermore, a quantitative analysis on the cross-talk among different frequencies was provided as well. The experimental results confirm that the two-channel frequency division multiplexing confocal fluorescence technology can not only maintain the high spatial resolution, but also realize the multiple points detection simultaneously with high temporal resolution (within millisecond level range), which benefits the dynamic studies of living biological cells.     

用于数码三维衍射图像的激光照排系统

研制了一种新型的用于数码三维衍射图像与光学可变图像的激光照排系统,采用空间光调制器(SL M)和全息干涉成像光学头进行子图输入和干涉条纹产生,系统在6 35 dpi图像分辨率下的运行效率达2 0 0 0 dot/s以上,该系统将为高效率制作2 D,2 D/3D和3D光变图像提供一种良好的工具。     

Digital Stroboscopic Holography Setup for Deformation Measurement at Both Quasi-Static and Acoustic Frequencies

A setup for digital stroboscopic holography that combines the advantages of full-field digital holographic interferometry with a high temporal resolution is presented. The setup can be used to identify and visualize complicated vibrational patterns with nanometer amplitudes, ranging from quasi-static to high frequency vibrations. By using a high-energy pulsed laser, single-shot holograms can be recorded and stability issues are avoided. Results are presented for an acoustically stimulated rubber membrane and the technique is evaluated by means of an accuracy and a repeatability test. The presented technique offers wide application possibilities in areas such as biomechanics and industrial testing.     

Application of Laser and Holographic Interferometry to Vibrational Investigations of Complex Three-Dimensional Constructions

Investigations of a pipeline of complex configuration made it possible to analyze the possibilities of laser and holographic interferometry methods in studies of strains of three-dimensional constructions under the effect of vibrational loads. The combined application of the holographic method of induced fringes, the method of recording the amplitude–frequency characteristics of object's vibrations using a laser interferometer, and the method of recording holographic interferograms averaged in time was considered. The most dangerous resonance frequencies and pipeline sections, in which its material is subjected to maximum stresses, were revealed.     

数字全息存储噪声分析

数字全息存储技术因具有能实现海量存储、可并行读出和超高速传输等特点而成为当今世界上的热门研究课题。目前,IBMAlmaden研究中心已经能够实现250GB/in2的数据存储密度。然而,由于存在各种噪声,导致误码率还比较高。首先介绍数字全息存储的基本原理,然后分析了存储过程的噪声来源以及抑制各类噪声的方法。尤其针对页内串扰噪声的抑制,介绍了像元误匹配补偿后处理技术。     

Optimizing multiphoton fluorescence microscopy light collection from living tissue by noncontact total emission detection (epiTED)

A benefit of multiphoton fluorescence microscopy is the inherent optical sectioning that occurs during excitation at the diffraction-limited spot. The scanned collection of fluorescence emission is incoherent; that is, no real image needs to be formed on the detector plane. The nearly isotropic emission of fluorescence excited at the focal spot allows for new detection schemes that efficiently funnel all attainable photons to detector(s). We previously showed [Combs, C.A., et al. (2007) Optimization of multiphoton excitation microscopy by total emission detection using a parabolic light reflector. J. Microsc. 228, 330-337] that parabolic mirrors and condensers could be combined to collect the totality of solid angle around the excitation spot for tissue blocks, leading to ～8-fold signal gain. Using a similar approach, we have developed an in vivo total emission detection (epiTED) instrument modified to make noncontact images from outside of living tissue. Simulations suggest that a ～4-fold enhancement may be possible (much larger with lower NA objectives than the 0.95 NA used here) with this approach, depending on objective characteristics, imaging depth and the characteristics of the sample being imaged. In our initial prototype, 2-fold improvements were demonstrated in the mouse brain and skeletal muscle as well as the rat kidney, using a variety of fluorophores and no compromise of spatial resolution. These results show this epiTED prototype effectively doubles emission signal in vivo; thus, it will maintain the image signal-to-noise ratio at two times the scan rate or enable full scan rate at approximately 30% reduced laser power (to minimize photo-damage).     

A comparison of digital holographic microscopy and on-axis phase-shifting interferometry for surface profiling

This paper presents a quantitative comparison between off-axis digital holographic microscopy (DHM) and on-axis phase-shifting interferometry (PSI) for surface micro topography measurement. The comparison has been applied on an object of a 1.34 μm nominal step height. The experimental results show that single shot, dual-wavelength, off-axis DHM surpasses on dual-wavelength, on-axis PSI in terms of accuracy and repeatability.     

Laser vibrodiagnostics of nonhomogeneous materials

The influence of nonhomogeneous material areas on the natural frequencies and interference pattern of vibrations of thin plates is analyzed by the speckle pattern and the holographic interferometry methods and the results are discussed. The dependence of the natural frequency bias and the vibration amplitude of the plate on the location of the nonhomogeneity has been researched taking into account excitation of the higher modes of vibration. It is shown that the natural vibration bias was maximum if the center of nonhomogeneity was located at the amplitude maximum of the vibrating plate. The sign of the frequency bias characterizes the prevailing influence of the relative change of density or rigidity of the plate. As shown from iterferograms obtained by the time-average holographic method the influence of heating with an infrared laser beam led to distortion of the interference pattern, which bears witness to the change of vibration form of the plate and the appearance of new amplitude maxima. The vibrations of nonhomogeneous areas have been examined by holographic interference microscopy.