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

Course Description This is an advanced course in which we explore the field of Statistical Optics. Topics covered include such subjects as the statistical properties of natural (thermal) and laser light, spatial and temporal coherence, effects of partial coherence on optical imaging instruments, effects on imaging due to randomly inhomogeneous media, and a statistical treatment of the detection of light. Development of this more comprehensive model of the behavior of light draws upon the use of tools traditionally available to the electrical engineer, such as linear system theory and the theory of stochastic processes.

http://ieeexplore.ieee.org/iel5/3/23094/01073023.pdf

Statistical optics

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

Thermophysical Properties Research Literature Retrieval Guide Edited by Y. S. Touloukian, J. K. Gerritsen and N. Y. Moore Second edition, revised and expanded. Book 1: Pp. xxi + 819. Book 2: Pp.621. Book 3: Pp. ix + 1315. (New York: Plenum Press, 1967.) n.p.

/pdf/heat-and-mass-transfer-1yaijfx8vp.pdf

Heat and Mass Transfer

The paper presents the recent contributions to the automatic fringe pattern analysis by the phase stepping method applied to moire interferometry. Two approaches are considerd. The first one is suitable for analysis of stable fringes directly in the moire interferometry set-up where a polarizing phase shifter is used. The second one is applied while unstable conditions during the experiment are encountered or a transient event is tested. This approach requres recording of an intermediate fringe pattern with carrier frequency and examining it in an additional double-diffraction or "sandwich"-type analyser. The experimental results of the analysis performed in the arrangements mentioned above are presented.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Automatic Fringe Pattern Analysis For Moire Interferometry

We present a holographic tomography technique in which the projections are acquired using both wavelength and illumination scanning in the near-infrared region. We show how to process the acquired data to obtain correct values of three-dimensional refractive index distributions in both single-wavelength and multi-wavelength data acquisition schemes and how to properly account for the dispersion of the sample. We perform numerical and experimental comparisons of different illumination scenarios to determine the most efficient measurement protocol. We show that the multi-wavelength protocol is advantageous in terms of signal-to-noise ratio and contrast-to-noise ratio over single-wavelength protocols, even for the same number of projections used for reconstructions. Finally, we show that this approach is suitable for providing high-quality refractive index distributions of relatively thick colon cancer samples.

Near-infrared, wavelength, and illumination scanning holographic tomography.

In the paper the concept of interactive implementation of grating interferometry and FEM is proposed in order to provide additional information to properly design and control both numerical and experimental procedures. At first the information from global FEM approximate model is used to design interferogram and adjust experimental setup. Having the best fitted experimental conditions, the measurement is performed. The results are used to improve the FEM parameters e.g. size and shape of FEM grid and fit local experimental data to modified FEM model. To provide the proper experimental tool, grating interferometry with two-channel acquisition module (for instantaneous u and v displacement measurement) is applied. The concept is tested on the examples of analysis of bending ceramic-to-metal joint and laser beam weldment under tensile semiaxial load.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Hybrid FEM/grating interferometry analysis of displacement fields in mechanical elements

In this paper we present the novel design and proof of concept of an active holographic camera consisting of two array detectors and Liquid Crystal on Silicon (LCOS) Spatial Light Modulator (SLM) The device allows sequential or simultaneous capture of two Fresnel holograms of 3D object/scene The two detectors configuration provides an increased viewing angle of the camera, allows to capture two double exposure holograms with different sensitivity vectors and even facilitate capturing a synthetic aperture hologram for static objects The LCOS SLM, located in a reference arm, serves as an active element, which enables phase shifting and proper pointing of reference beams towards both detectors in the configuration which allows miniaturization of the camera The laboratory model of the camera has been tested for different modes of work namely for capture and reconstruction of 3D scene and for double exposure holographic interferometry applied for an engineering object under load The future extension of the camera functionalities for Fourier holograms capture is discussed

Two detector, active digital holographic camera for 3D imaging and digital holographic interferometry

New image processing methods and active photonics apparatus have made possible the development of relatively inexpensive optical systems for complex shape and object measurements. We present dynamic 360° scanning method for analysis of human lower body biomechanics, with an emphasis on the analysis of the knee joint. The anatomical structure (of high medical interest) that is possible to scan and analyze, is patella. Tracking of patella position and orientation under dynamic conditions may lead to detect pathological patella movements and help in knee joint disease diagnosis. The processed data is obtained from a dynamic laser triangulation surface measurement system, able to capture slow to normal movements with a scan frequency between 15 and 30 Hz. These frequency rates are enough to capture controlled movements used e.g. for medical examination purposes. The purpose of the work presented is to develop surface analysis methods that may be used as support of diagnosis of motoric abilities of lower limbs. The paper presents algorithms used to process acquired lower limbs surface data in order to find the position and orientation of patella. The algorithms implemented include input data preparation, curvature description methods, knee region discrimination and patella assumed position/orientation calculation. Additionally, a method of 4D (3D + time) medical data visualization is proposed. Also some exemplary results are presented.

Malgorzata Kujawinska

Papers

Automatic Fringe Pattern Analysis For Moire Interferometry

Near-infrared, wavelength, and illumination scanning holographic tomography.

Hybrid FEM/grating interferometry analysis of displacement fields in mechanical elements

Two detector, active digital holographic camera for 3D imaging and digital holographic interferometry

Automatic anatomical structures location based on dynamic shape measurement