Dual plane in-line digital holographic microscopy

We report a dual plane in-line digital holographic microscopy technique that exploits the method of subtraction of average intensity of the entire hologram to suppress the zero-order diffracted wave. Two interferograms are recorded at different planes to eliminate the conjugate image. The experimental results demonstrate successful reconstruction of phase objects as well as of amplitude objects. The two interferograms can be recorded simultaneously, using two CCD or CMOS sensors, in order to increase the acquisition rate. This enhanced acquisition rate, together with the improved reconstruction capability of the proposed method, may find applications in biomedical research for visualization of rapid dynamic processes at the cellular level.     

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.     

A method for increasing the sensitivity of determination of the wavefront distortion in optical processing of holographic lateral shear interferograms

A method for obtaining interference patterns of increased sensitivity in optical processing of holographic lateral shear interferograms recorded under linear conditions at a shear exceeding the size of a phase object under study is proposed. Cases of reconstruction of interference patterns of increased sensitivity using matched and optically conjugate holographic lateral shear interferograms are considered. It is shown that two-and fourfold increases in sensitivity, respectively, are obtained in these cases. The validity of the method proposed is confirmed experimentally     

Enhancement of sensitivity of measurements of the holographic lateral-shear interferometry in studies of fast processes

The possibility of enhancing the sensitivity of measurements upon visualization of temporal variations of a phase object by means of optical processing of the holographic lateral-shear interferograms, without the necessity of detecting the original holographic interferograms under nonlinear conditions, is considered. In rewriting the original holographic interferogram, it is advisable to change the orientation of the holographic fringes and to record the secondary holograms under nonlinear conditions. The proposed method for increasing the sensitivity of measurements was used to visualize variations of thickness of a polymethyl methacrylate plate in the course of its thermal treatment.     

用实时全息术研究低速变化过程的一种简易系统

研制了一种用于研究物体低速过程的简易系统，它由带有液门原位化学处理的实时全息干涉装置和具有连拍功能的相机以及一台氦氮激光器组成，是一种简易实用的“低速、实时全息干涉摄影系统”。用它记录了火箭推进剂样品在室温，常压下的燃烧过程，１００瓦普通只灯逐级加压的点燃过程，对实时全息图的记录和处理采用了一种可获得高反衬度的新技术，拍摄的成功率高，干涉条纹的反衬度好，它为研究物体的低速变化过程提供了一种有力的手     

Enhancement of the measurement sensitivity in multiple-exposure holographic interferometry

Specific features of reconstruction of enhanced-sensitivity interferograms in the optical processing of a multiple-exposure hologram recorded under linear conditions are considered. To enhance the measurement sensitivity when visualizing the changes in the state of an object under study that take place during the time between exposures, it is proposed that the holographic structures corresponding to these exposures on a new carrier be rewritten and the double-exposure hologram thus obtained under nonlinear conditions be recorded. The proposed technique of enhancement of the measurement sensitivity was experimentally tested when visualizing a change of the temperature field in a flat glass plate.     

二次曝光全息术对微波等离子体推进器羽流的诊断及计算机模拟

二次曝光全息术是诊断等离子体电子数密度的一个有效测量方法,具有非接触式测量及不受等离子体发光干扰等优点.根据阿贝尔变换公式,通过计算机应用matlab程序数值模拟了各种不同电子数密度状态下的等离子体干涉图.同时拍摄了航天器中微波等离子体推进器羽流的二次曝光全息图,再现了不同状态下的干涉图样.通过分析和对比两次干涉图,得出了羽流的电子数密度.     

Non-destructive evaluation of materials at high temperatures using electro-optic holography

An electro-optic holographic technique for the non-destructive evaluation of materials at high temperatures is presented. The test object is heated in an oven that can attain a temperature of 1000 °C. Electro-optic holography is used for the real-time visualization of full field in-plane displacement fringes. Digital image processing techniques are used for the analysis of fringes. Some of the problems encountered, while recording interferograms at high temperatures, are discussed. The technique is employed for the measurement of in-plane strains, in a disc of a super alloy, subjected to diametral compression, at 1000 °C.     

Interferometrie a double plage par photographie “speckle”

The image of a partial diffusor is recorded on a holographic plate. After development, the hologram is repositioned to observe “live fringes”. Half of the aperture of the optical system has been masked during the exposure, but the full aperture is used for the reconstruction. Two separate reconstructed images of the half aperture show two different interferograms. This set up can be used to measure displacements of objects, or defocusing.     

Holographic reverse shearing interferometry with high measurement sensitivity

The possibility of studying phase objects by reverse shearing interferometry with high measurement sensitivity is demonstrated. Phase objects are studied in two stages. In the first stage, holographic reverse shear interferograms are measured with and without an object under nonlinear conditions with tuning to frequent reference fringes. In the next stage, these interferograms are optically processed to obtain two interference patterns. The behavior of the interference fringes is the same as in the case of conventional double-beam interferometry with a standard reference wave. The increase in the measurement sensitivity in the thus-obtained interference patterns is due to the use of higher diffraction orders reconstructed from the holographic interferograms. A possibility of controlling the width of interference fringes is considered. The results of experimental approval of this technique are presented.     

A compact holographic interferometer with a single optical element

A compact holographic interferometer is presented. A key feature of the instrument is the minidiffuser used as a single optical element. Divergent diffuse waves formed on illumination of the minidiffuser by a narrow beam from a continuous wave (CW) laser are shown to be well suited for obtaining high-quality reflection holographic interferograms and holograms.     

Extension of the controlled sensitivity range in holographic interferometry with a lateral shear

The possibility of controlling the measurement sensitivity in shearing interferometry with a small lateral shear is considered. A method based on recording several holographic interferograms with different magnitudes of lateral shear and with different carrier frequencies of holographic fringes during a single exposure is proposed. The measurement sensitivity of the interference patterns is controlled at the stage of optical processing of the combined holographic interferograms with lateral shear, when the interferograms are illuminated by two coherent light beams and the filtering of the corresponding diffraction orders is performed. The results of the experimental testing of the proposed method by using it for the visualization of the melting zones of planar polymethylmethacrylate samples under heat treatment are presented.     

Evaluation of residual deformations generated by a pulsed ion implanter using interferometric phase measurement

A Fourier transform method of holographic fringe pattern analysis is applied to measure surface residual deformations generated by a pulsed ion implanter. The technique uses a fixture that makes it possible to remove the specimen and put it back into the same position after being implanted. The phase information from interferograms extracted by means of the Fourier transform method is unwrapped using an algorithm based on cellular automata. Results computed from the application of a numerical model are compared with those determined experimentally and a reasonable agreement is obtained.     

Recent contribution in color interferometry and applications to high-speed flows

Recent improvements brought to color interferometry for analyzing high-speed flows are described through different applications. First, the optical technique based on differential interferometry using a polarized white light and one or two Wollaston prisms allows to record high-speed interferograms of the flow downstream of a circular cylinder. Then, this technique has been applied to axisymmetric flows for studying an interaction between a supersonic hot jet and a coaxial supersonic flow. Another application concerns the study of hypersonic flows using Wollaston prisms with a large birefringence angle. Finally, the analysis of gaseous mixture and the evolution of two-gases interface submitted to an acceleration is presented. Interferograms analysis is made from a modeling of interference fringes versus the optical path difference which allows to easily extract quantitative information of the gas density. In order to obtain absolute measurements of the gas density, real-time holographic interferometry has been developed using a three-color laser source and a panchromatic holographic plate. The technique generates the achromatic white fringe which makes the zero order of interference fringes easy to identify. An application is presented in a 2D subsonic wind tunnel, in which the unsteady wake flow past a cylinder is recorded at high framing rate. In this optical setup, transmission holograms are used. As a conclusion, an approach is proposed to analyze the 3D flows from real-time color holographic interferometry using reflection holograms and the problems to solve are described.     

The measurement of 3-D asymmetric temperature field by using real time laser interferometric tomography

A real time nondestructive temperature measurement technique based on laser holographic interference tomography technique is presented. An He–Ne laser is used as light source, and a CCD video camera is used to grab the interferogram. This laser holographic tomography technique is applied to the measurement of the temperature fields generated by two heated rods. Since data error is inevitable in engineering measurement, it is necessary to study the reconstruction techniques for reconstructing the temperature field. Three techniques including convolution back projection (CBP), algebra reconstruction technique (ART) and simultaneous iterative reconstruction technique (SIRT) are studied. Based on the reconstruction techniques and experimental situation, ART is used to reconstruct the asymmetric temperature fields. The thermocouples are used to measure the temperatures of the two heated rods. Comparing the reconstructed result with the measured temperature value, a satisfactory result is obtained.     

Visualized measurement of the acoustic levitation field based on digital holography with phase multiplication

By using digital holographic interferometory with phase multiplication, the visualized measurement of the acoustic levitation field (ALF) with single axis is carried out. The digital holograms of the ALF under different conditions are recorded by use of CCD. The corresponding digital holographic interferograms reflecting the sound pressure distribution and the interference phase distribution are obtained by numerical reconstruction and phase subtraction, which are consistent with the theoretical results. It indicates that the proposed digital holographic interferometory with phase multiplication can successfully double the fringe number of the interference phase patterns of the ALF and improve the measurement precision. Compared with the conventional optical holographic interferometory, digital holographic interferometory has the merits of quasi real-time, more exactitude and convenient operation, and it provides an effective way for studying the sound pressure distribution of the ALF.     

Multiple-exposure high-sensitivity holographic interferometry for studying moving objects

A method for increasing the sensitivity of measurements through aberration compensation upon reconstruction of interferograms from two multiple-exposure holograms is proposed. At the early stage of object investigation, the holographic structures recorded at certain time instants are rerecorded by two coherent beams on new image carriers. In this case, the interference moiré method is employed to monitor the equality of the vectors of the holographic structures rerecorded. At the final stage, the new nonlinear holograms are processed in an optical analyzer of conjugate holograms with the use of incoherent light. The hologram thus reconstructed offers a high sensitivity of measurements and is free of aberrations. The method is tested by visualizing the temperature-field variations in a glass substrate with a conducting coating.     

Measurement of non-monotonous phase changes in temporal speckle pattern interferometry using a correlation method without a temporal carrier

Recently, a phase evaluation method was proposed to measure nanometric displacements by means of digital speckle pattern interferometry when the phase change introduced by the deformation is in the range [0,π) rad. This method is based on the evaluation of a correlation coefficient between two speckle interferograms generated by both deformation states of the object. In this paper, we present a novel technique to measure non-monotonous displacements in temporal speckle pattern interferometry using a correlation method without a temporal carrier. In this approach, the sign ambiguity is resolved automatically due to the introduction of a function that determines the correct sign of the displacement between two consecutive speckle interferograms. The rms phase errors introduced by the proposed method are determined using computer-simulated speckle interferograms. An application of the phase retrieval method to process experimental data is also presented.     

Speckle interferometry

Illumination of a rough surface by a coherent monochromatic wave creates a grainy structure in space termed a speckle pattern. It was considered a special kind of noise and was the bane of holographers. However, its information-carrying property was soon discovered and the phenomenon was used for metrological applications. The realization that a speckle pattern carried information led to a new measurement technique known as speckle interferometry (SI). Although the speckle phenomenon in itself is a consequence of interference among numerous randomly dephased waves, a reference wave is required in SI. Further, it employs an imaging geometry. Initially SI was performed mostly by using silver emulsions as the recording media. The double-exposure specklegram was filtered to extract the desired information. Since SI can be configured so as to be sensitive to the in-plane displacement component, the out-of-plane displacement component or their derivatives, the interferograms corresponding to these were extracted from the specklegram for further analysis. Since the speckle size can be controlled by the F number of the imaging lens, it was soon realized that SI could be performed with electronic detection, thereby increasing its accuracy and speed of measurement. Furthermore, a phase-shifting technique can also be incorporated. This technique came to be known as electronic speckle pattern interferometry (ESPI). It employed the same experimental configurations as SI. ESPI found many industrial applications as it supplements holographic interferometry. We present three examples covering diverse areas. In one application it has been used to measure residual stress in a blank recordable compact disk. In another application, microscopic ESPI has been used to study the influence of relative humidity on paint-coated figurines and also the effect of a conservation agent applied on top of this. The final application is to find the defects in pipes. These diverse applications demonstrate the power of this technique.     

Analysis of holographic interferograms with a tv picture system

An automatic dual reference beam method for the evaluation of holographic interferograms is presented. Based on the principle of image intensity subtraction, the method employs video electronic recording of the interograms and high speed digital image processing. Quantitative results are given for the bending of a cantilever.