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

Error in speckle photography:Effect of coherent and incoherent speckles.

In this paper a comparison of different techniques to obtain vibration patterns by phase stepping on an electronic speckle pattern interferometer (ESPI) is made. The theoretical evaluation of the contrast of the fringes shows that the (pi) phase step method gives good contrast; however, the four step method gives the same contrast along with better pictorial representation. Speckle averaging on the other hand also increases the contrast of the fringes apart from smoothing of speckles. Experimental results corroborating the theoretical predictions are also presented.

Electronic speckle pattern interferometric vibration fringes

A technique to record rainbow holograms in a single step is described. The technique is based on the realisation of a synthetic slit. The synthetic slit with low side-lobes is generated by multiple exposures; The imaging lens is translated discretely between exposures. Finer slit is realised by increasing the number of exposures.

One Step Rainbow Holography Using Synthesized Slit with Low Side-Lobes

Multiplexing in speckle shear interferometry: an optimal method.

The Department of Physics and Optical Engineering at Rose-Hulman Institute of Technology has served as an educational outreach partner with the National Science Foundation sponsored engineering research center, Lighting Enabled Systems & Applications (formally Smart Lighting) for the past eight years. As part of the center, we developed educational materials on smart lighting, developed and taught lighting courses and workshops for both high school teachers and college students, and produced several short educational videos with students on lighting and general optical engineering topics. In this paper we will give examples of research and technical projects that were completed with students, discuss instructional materials that were developed, and describe the content of lighting and optics related educational videos.

/pdf/lighting-education-and-outreach-at-rose-hulman-institute-of-4irmostzt2.pdf

Charles Joenathan

Papers

Error in speckle photography:Effect of coherent and incoherent speckles.

Electronic speckle pattern interferometric vibration fringes

One Step Rainbow Holography Using Synthesized Slit with Low Side-Lobes

Multiplexing in speckle shear interferometry: an optimal method.

Lighting education and outreach at Rose-Hulman Institute of Technology