Model of holographic recording in thermoplastic materials

A method for the evaluation of images reconstructed from holograms recorded in thermoplastic materials is reported. The method is based on the use of the experimental modulation transfer function and nonlinear holographic characteristics of the recording material. Calculations have been carried out for high-numerical-aperture holograms of a five-element Ronchi ruling. The quality of the reconstructed image as a function of the recording parameters has been computed. The model predicts that it is possible to optimize holographic recording in these materials.     

Development of a phase-displacement equation for panoramic interferometry

We developed the parametric equations that are needed to quantify the modulations in the sensitivity vector that occur when the phase-displacement equation is applied to make panoramic interferometric measurements. The measurement system relies on two collinear panoramic annular lenses, one to illuminate and the other to image their surroundings. When a coherent light source is used and a reference beam is added, interference occurs over the region of interest defined by the illuminating and viewing lenses. A holographic system is used to demonstrate the approach and quantify the analysis. We obtained interference fringes in real time by comparing holograms recorded before and after a section of cylindrical pipe is displaced relative to the measurement system. The annular images and the holographic fringes are acquired and stored digitally in a computer system, and image transformation algorithms are applied to remove optical distortions in the holographic patterns. Excellent agreement is obtained when the fringe loci are compared with those predicted on the basis of theory.     

Large-sized Holographic Interferometry in Real Image

The recording of large holograms has been performed on photographic plates up to 1·5m². Applied to holographic interferometry, this achievement permits the analysis of holographic real images of large models and the recording of the topography of interference fringes.     

Holographic imaging and interferometry with non-Bragg diffraction orders on volume and surface-relief gratings in lithium niobate and photo-thermoplastic materials

The recording of holographic volume and surface-relief gratings in a photorefractive crystal using a photo-thermoplastic (PTP) holographic camera with an image-bearing signal beam leads to the appearance of two Bragg and two or more non-Bragg diffracted beams that show the transformed images in each beam (rotation and angular amplification of images). Using this real-time mode of interferometry, the hologram is retrieved with a deformed object beam, resulting in the appearance of fringes with a proper phase shift in each of four diffracted beams. This one-shot (one-exposure) phase-shifting interferometry results in clarification of the object wave-front information (for example, from surface deformation) and solution of the sign ambiguity problem. This procedure demonstrates that high-resolution holographic imaging of the PTP holographic camera static deformations in the order of ～0.1?mm can be revealed on the diffusion reflection surface. In addition, it was demonstrated that using the PTP materials could achieve holographic recording and imaging through phase aberration, with the image appearing in the non-Bragg diffraction order.     

Method for fringe enhancement in holographic interferometry for measurement of in-plane displacements

Theoretical background along with experimental results are given for a simple method for in-plane fringe enhancement in dual-beam illumination holographic interferometry. In this method, the fringes representing in-plane displacements arise as a moirépattern between two interferograms. To distinguish the in-plane displacement, a sequence of images is recorded while the reference mirror is continuously tilted at random. The in-plane fringes arethen found as the maximum contrast of the out-of-plane fringes in the image sequence. The resulting fringe quality is close to the quality of the out-of-plane fringes.     

Optical fringe multiplication in moiré interferometry

An optical method for multiplication of moiré fringes is proposed to increase the sensitivity of moireé interferometry. The process involves two recording steps. In the first step, a traditional moiré interferometry setup is used. The moiré pattern containing carrier fringes and load fringes is recorded onto a glass-based holographic plate. The carrier frequency is much lower than that of the original specimen grating. The plate is then developed. In the second step, the holographic plate, regarded as a distorted specimen grating, is further examined by a similar moiré interferometry system. The frequency of the second virtual grating is arranged to be 2n times that of the carrier fringes contained in the recorded plate. As a result, the load fringes are revealed with a multiplication factor of 2n. The interpretation of the optical multiplication method from wave-front interference theory is given and an experiment is conducted.     

Comparative study of various endoscopes for pulsed digital holographic interferometry

A comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5-600 micros). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult.     

Resonant holographic interferometry with ZnTe:V:Mn

The photorefractive semiconductor ZnTe:V:Mn is investigated for use in real-time resonant holographic interferometry applications. Experimental results of two-wave and four-wave mixing with pulsed dye and cw diode lasers are presented; in addition holographic image transfer, as well as two-wavelength resonant holographic interferometry, are demonstrated. Species-specific interferograms of potassium seeded into various combustion environments are captured at video-frame rates. Calculations of the species measurement sensitivity and dynamic range are presented, and design considerations for resonant holographic interferometry systems employing photorefractive materials are outlined.     

希尔伯特变换实时全息干涉条纹相位提取

实时全息干涉法可以观察记录整个测试过程中条纹图的动态变化,传统相位提取算法只适合于静态干涉条纹图相位的提取.根据实时全息干涉条纹和希尔伯特变换的特点,提出了利用希尔伯特变换提取实时全息干涉条纹相位值的方法,采用了高通滤波的方法减少背景光强的影响,对铝片受力变形实验中实时全息干涉条纹的相位变化分布进行了提取.实验表明:希尔伯特变换法适合于动态条纹的相位提取,可以自动提取实时全息干涉测量过程中全场各点在任意两个时刻间的相位变化值,且测量结果与实时全息干涉条纹人工分析结果一致.     

Digital recording and numerical reconstruction of lensless fourier holograms in optical metrology

Advantages of the lensless Fourier holography setup for the reconstruction of digitally recorded holograms in holographic interferometry are presented. This very simple setup helps to achieve a maximum lateral resolution of the object under investigation. Also, the numerical-reconstruction algorithm is very simple and fast to compute. A mathematical model based on Fourier optics is used to describe discretization effects and to determine the lateral resolution. The recording and the reconstruction processes are regarded as an optical imaging system, and the point-spread function is calculated. Results are verified by an experimental setup for a combined shape and deformation measurement.     

Digital recording and reconstruction of holograms in hologram interferometry and shearography

The fundamentals of digital recording and mathematical reconstruction of Fresnel holograms are described. The object is recorded in two different states, and the holograms are stored electronically with a charge-coupled-device detector. In the process of reconstruction the digitally sampled holograms are applied to the different coherent optical methods as hologram interferometry and shearography. If the holograms are superimposed and reconstructed jointly, a holographic interferogram results. If a shearing is introduced in the reconstruction process, a shearogram results. This means that the evaluation technique, e.g., hologram interferometry or shearography, can be influenced by numerical methods.     

Real-time holographic baseband frequency demodulator

The multiplicative and low-bandpass filtering characteristics of real-time holograms in photorefractive media are used as a basis for a baseband frequency demodulator by means of holographic homodyne detection. We experimentally demonstrate the demodulation of spatial bandpass signals in the kilohertz regime and homodyne detection in the gigahertz regime.     

Digital holographic interferometry for simultaneous orthogonal radial vibration measurements along rotating shafts

A digital holographic interferometry setup used to measure radial vibrations along a rotating shaft is presented. A continuous Nd:YAG laser and a high-speed digital camera are used for recording the holograms. The shaft was polished optically smooth to avoid speckle noise from the rotating surface. The light reflected from the shaft was directed onto a diffuser which in turn was imaged by the holographic system. Simultaneous measurements with a laser vibrometer were performed at one point and comparisons between the signals showed good agreement. It is shown that different vibration components of a rotating shaft can be simultaneously measured with this technique.     

Removal of bias and the conjugate image in incoherent on-axis triangular holography and real-time reconstruction of the complex hologram

We present and experimentally test a new passive-device incoherent holographic system that removes the bias and the conjugate image. The system is based on the triangular interferometer with the modification of insertion of simple passive devices and can easily be extended for obtaining real-time complex holograms without bias and conjugate images for moving objects. A scheme for real-time reconstruction of the complex hologram is also presented and experimentally tested.     

Double-exposure phase calculation method in electronic speckle pattern interferometry based on holographic object illumination

Multiple-exposure phase calculation procedures are widely used in electronic speckle pattern interferometry to calculate phase maps of displacements. We developed a double-exposure process based on holographic illumination of the object and the idea of the spatial carrier phase-shifting method to examine transient displacements. In our work, computer-generated holograms and a spatial light modulator were used to generate proper coherent illuminating masks. In this adjustment all phase-shifted states were at our disposal from one recorded speckle image for phase calculation. This technique can be used in the large scale of transient measurements. In this paper we illustrate the principle through several examples.     

Real-time speckle interferometry fringe formation with an adaptive phase mask

We describe what we believe is a novel speckle-pattern interferometry method of applying a spatial light modulator (SLM) as an adaptive phase mask to obtain real-time fringes of a deformed object without using conventional correlation methods of electronic subtraction or addition. The method is to use a SLM to cancel initial phase in the speckled image before the object is deformed. The fringes from the deformed object can be visualized directly after the initial phase has been canceled. A commercial liquid-crystal television is used as a SLM. The performance of using this SLM in an out-of-plane speckle interferometer is demonstrated.     

Model for the effects of material shrinkage on volume holograms

A model for analyzing the effects of material shrinkage on volume holograms is presented. This model is based on the fringe-plane rotation model used for describing the effects of plane-wave grating holograms that undergo shrinkage. A computer was used to exercise the model for a simple input object typical of those used in digital holographic memory applications and stored as a Fourier-transform hologram. The theoretical formulation of the model is presented as well as the results of the numerical analysis.     

Phase-conjugate resonant holographic interferometry applied to NH concentration measurements in a two-dimensional diffusion flame

Resonant holographic interferometry is a diagnostic technique based on the dispersion of light having a frequency close to that of an electronic transition of a molecule. We propose a novel single-laser, two-color setup for the recording of resonant holograms and apply it to two-dimensional (2D) species concentration measurements in a combustion environment. The generation of the second color is achieved by optical phase conjugation from stimulated Brillouin scattering in a cell. The frequency shift of ~8.5 GHz introduced by the phase conjugation matches approximately the linewidth of many molecular transitions at typical flame temperatures and can be implemented to produce holograms of good contrast and diffraction efficiency. Phase-conjugate resonant holographic interferometry is demonstrated in a 2D NH(3) -O(2) flame, yielding interferograms containing information on the NH radical concentration distribution in the flame. Experimental results are quantified by application of a numerical computation of the complex refractive index.     

Contouring of diffused objects using lensless Fourier transform digital moiré holography

A method is proposed for contouring of diffused objects using digital holographic moiré interferometry in lensless Fourier transform configuration. Fringe projection moiré technique combined with digital double-exposure holography produces the contours in this method. Two digital holograms of a 10?mm aluminum alloy cube are recorded by tilting the illumination angle slightly between exposures, and a third one is recorded by translating the detector a little laterally with the final illumination angle unchanged. Upon numerical processing of the first two holograms, a plane parallel fringe system seems to be projected onto the object. This fringe system can be referred to as the modified grid. Processing of the second and the third hologram results in another grid, the reference grid. In effect, processing of the first and the third hologram combines the modified and the reference grids to produce the moiré contour fringes. The range of contour intervals obtained remains between 2.73 and 0.38?mm with seven different contours in between. The present method can measure details of a great variety of sizes on objects of large dimensional range. Deviations in the measured contour intervals from the theoretically calculated values are found to be within 12%-18%. This seems to be because of the deviation in the present experimental geometry from the ideal theoretical configuration, the hologram digitization, and the particular reconstruction algorithm used in the present experimental arrangement.     

The application of two-refractive-index contouring on the contour difference of two compared specimens

The development of comparative holographic Moire interferometry is accelerated by the need for nondestructive evaluation. It is based on a comparison of a master and test objects and a visualization of the difference in the mechanical responses under identical loading condition. In this paper, the hybrid method of comparative holographic Moire interferometry and the two-refractive-index contouring technique are used to generate contour difference for two compared specimens. The interference pattern of the master and test specimens are superimposed by a reconstruction beam. Moire fringes, produced between the two interference patterns, outline the contour differences in the compared specimens. The proposed experimental approach provides an advantage that full knowledge of the optical arrangement during construction and reconstruction of the hologram does not have to be accurately available. A partial-spherical object and its rotated status were simulated as the master and test objects.