Charles Joenathan

Bio: Charles Joenathan is an academic researcher from Rose-Hulman Institute of Technology. The author has contributed to research in topics: Interferometry & Speckle pattern. The author has an hindex of 18, co-authored 103 publications receiving 1542 citations. Previous affiliations of Charles Joenathan include University of Stuttgart & Indian Institutes of Technology.

Speckle interferometry with temporal phase evaluation for measuring large-object deformation

Abstract: We propose a new method for measuring large-object deformations by using temporal evolution of the speckles in speckle interferometry. The principle of the method is that by deforming the object continuously, one obtains fluctuations in the intensity of the speckle. A large number of frames of the object motion are collected to be analyzed later. The phase data for whole-object deformation are then retrieved by inverse Fourier transformation of a filtered spectrum obtained by Fourier transformation of the signal. With this method one is capable of measuring deformations of more than 100 μm, which is not possible using conventional electronic speckle pattern interferometry. We discuss the underlying principle of the method and the results of the experiments. Some nondestructive testing results are also presented.

Phase-measuring interferometry: new methods and error analysis

Abstract: New methods that can be used to determine phase in phase-stepping interferometry are presented. It is shown that a combination of some of these methods can be used to reduce the error introduced by phase-stepper miscalibration and nonlinearity. Moreover these new algorithms can also be used to detect the presence of miscalibration or phase-shifter nonlinearity. A simplified approach to understanding the error introduced by miscalibration and nonlinearity of the phase stepper and its reduction in phase-shifting interferometry is also presented.

Temporal and spatial properties of the time-varying speckles of botanical specimens

Abstract: Techniques for measuring time-varying biospeckle of botanical specimens are investigated. Experimental evidence on the probability density function is presented. Several applicable techniques, such as power spectral density and correlation, are used for measuring and analyzing the temporal speckle intensity variations. These techniques are shown to exhibit information about the shelf life and aging of some botanical specimens used in our study. We also present a new phenomena related to the spatial properties of time-varying speckles. Theoretical and experimental results on the size of a speckle in a speckle pattern and its relation to the temporal intensity variation are also detailed.

Contouring by electronic speckle pattern interferometry employing dual beam illumination

Abstract: In this paper we extend and study the method for generating contours of diffuse objects employing a dual beam illumination coupled with electronic speckle pattern interferometry. The sensitivity and the orientation of the contour planes are analyzed. A novel method for tilting the planes of contours and experimental results incorporating phase shifting and fringe analysis are also presented. The theoretical and the experimental results show good agreement.

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

Abstract: 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.

Overview of three-dimensional shape measurement using optical methods

Abstract: 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)

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Abstract: 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.

Properties and Applications of Colloidal Nonspherical Noble Metal Nanoparticles

Abstract: 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.

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

Abstract: 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.