A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Nanoparticles of noble metals belong to the most extensively studied colloidal systems in the field of nanoscience and nanotechnology. Due to continuing progress in the synthesis of nanoparticles with controlled morphologies, the exploration of unique morphology-dependent properties has gained momentum. Anisotropic features in nonspherical nanoparticles make them ideal candidates for enhanced chemical, catalytic, and local field related applications. Nonspherical plasmon resonant nanoparticles offer favorable properties for their use as analytical tools, or as diagnostic and therapeutic agents. This Review highlights morphology-dependent properties of nonspherical noble metal nanoparticles with a focus on localized surface plasmon resonance and local field enhancement, as well as their applications in various fields including Raman spectroscopy, fluorescence enhancement, analytics and sensing, photothermal therapy, (bio-)diagnostics, and imaging.

Properties and Applications of Colloidal Nonspherical Noble Metal Nanoparticles

Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

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Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

. A phase-measuring fiber optic electronic speckle pattern in- terferometer (ESPI) was recently constructed and demonstrated. In thisarrangement, phase stepping is introduced by stretching the fiber wrappedaround a piezoelectric transducer. Calibration of the phase step is criticalin phase measurement techniques for obtaining good phase plots. Meth-ods used for calibrating the stretcher are outlined and the drifts in thephase caused by fluctuations in temperature and mechanical stressesare discussed. Ways to minimize this drift are also presented. Subject terms: speckle interferometry; electronic speckle pattern interferometry.Optical Engineering 31(2), 315-321 (February 1992).phase step calibration is important in order to obtain error- free phase maps. Different methods for calibrating the piezoelectric transducer (PZT) in an interferometric arrangement13 as well as in a fiber optic interferometric sensor arrangement14 have been developed. Methods suchas phase-lock, sinusoidal extrema sensing, and employingsoftware routines to evaluate the phase from equations andintensity values are successful with specular interferometricfringes. On the other hand, the ESPI fringes are speckled.Even though good calibration can be obtained with phase-lock and sensing methods ,

Phase-measuring fiber optic electronic speckle pattern interferometer: phase step calibration and phase drift minimization

Speckle-shear interferometry with double dove prisms

Lateral shear interferometry with holo shear lens

This paper presents a number of methods to obtain in-plane displacement, out of plane displacement and slope data using holographic optical elements. The results obtained with a hololens and a holoshear lens are as good as those obtained with conventional optical systems.

Hololens in speckle and speckle shear interferometry.

This paper presents a method of eliminating the error introduced by the nonuniform diffraction halo in speckle photography. It is shown that, by proper aperturing of the imaging lens, the intensity distribution in the diffraction halo can be made constant over a certain frequency range. The measurements made on Young's fringes, present in this region, would be free from error due to varying intensity in the diffraction halo.

Charles Joenathan

Papers

Phase-measuring fiber optic electronic speckle pattern interferometer: phase step calibration and phase drift minimization

Speckle-shear interferometry with double dove prisms

Lateral shear interferometry with holo shear lens

Hololens in speckle and speckle shear interferometry.

Elimination of error in speckle photography.