R. Dändliker

Bio: R. Dändliker is an academic researcher from Brown, Boveri & Cie. The author has contributed to research in topics: Holography & Holographic interferometry. The author has an hindex of 8, co-authored 18 publications receiving 407 citations.

High resolution hologram interferometry by electronic phase measurement

Abstract: The described dual frequency method interpolates the fringe pattern of any kind of hologram interfermetry down to better than 1 100 of a fringe, independent of intensity variations. Experiments with double-exposure holography demonstrate a resolution of 6 × 10−4 fringes at any point of the object. Spatial derivatives of deformations can be measured accurately for mechanical strain analysis.

Hybrid optical and electronic image processing for strain measurements by speckle photography

Abstract: A Young's fringe processor for speckle photographs is described. It automatically measures fringe separation and orientation with an accuracy of 1% and 1 degrees , respectively. The fringe evaluation is fast and computer controlled. Fringe densities of one to twenty fringes within the diffraction pattern can be treated with the same resolution. Application to displacement and strain measurements by focused image speckle photography is reported. Local strains can be determined with an accuracy of ~E = 10(-5) for displacements between 10 and 100 microm and a spatial resolution of 10 mm.

I Heterodyne Holographic Interferometry

Abstract: Publisher Summary Interferometry is an old and very powerful technique to measure the deviation between two wavefields with a sensitivity of a fraction of a wavelength. In holographic interferometry, at least one of the wavefields to be compared interferometrically is stored in a hologram. The hologram is usually recorded experimentally with the help of a reference wave. However, computer-generated holograms constructed theoretically may also be used to supply special, previously not existing wavefields. In most cases, the hologram itself also acts as the beamsplitter for the superposition of the two wavefields. Holographic interferometry has some unique properties, which makes it superior to classical interferometry; wavefields from the same object, but under different conditions and at different times, can be compared. This is an essential prerequisite to compare interferometrically different states of solid objects with opaque, diffusely scattering surfaces. Transient wavefields can be frozen instantaneously by short exposure times. Time averaged wavefields can be recorded and compared afterward. This results in reduction of noise and increase of accuracy and stability.

A theoretical analysis of laser Doppler flowmeters

Abstract: A theoretical analysis is given of single and dual beam scattering flowmeters. All propagating beams are treated rigorously, taking their Gaussian characteristics into account. An exact derivation of the Doppler frequency shows how it depends on the position of the scattering particle within the scattering volume. The spatial and spectral resolutions of both Doppler systems are given. It is shown in what way these depend on the geometry of the optical arrangement. The average power spectrum of the detector signal is derived as a function of the particle concentration. The signal-to-noise ratios of both systems are calculated and compared. Some inherent differences between the two systems will be pointed out.

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.

Active optical range imaging sensors

Abstract: Active, optical range imaging systems collect three-dimensional coordinate data from object surfaces. These systems can be useful in a wide variety of automation applications, including shape acquisition, bin picking, assembly, inspection, gauging, robot navigation, medical diagnosis, cartography, and military tasks. The range-imaging sensors in such systems are unique imaging devices in that the image data points explicitly represent scene surface geometry in a sampled form. At least six different optical principles have been used to actively obtain range images: (1) radar, (2) triangulation, (3) moire, (4) holographic interferometry, (5) lens focusing, and (6) diffraction. The relative capabilities of different sensors and sensing methods are evaluated using a figure of merit based on range accuracy, depth of field, and image acquisition time.

Direct phase determination in hologram interferometry with use of digitally recorded holograms

Abstract: A new method of phase determination in hologram interferometry is described. The Fresnel holograms, which represent the undeformed and the deformed states of the object, are generated on a CCD target and stored electronically. No lens or other imaging device is used. The reconstruction is done from the digitally stored holograms with mathematical methods. It is shown that the intensity as well as the phase can be calculated from the digitally sampled holograms. A comparison of the phases of the undeformed and the deformed states permits direct determination of the interference phase.

The design of plasma etchants

Abstract: Theory and practice of plasma etching are critically reviewed. Some unifying principles are extended to explain a large body of experimental data, encompassing more than 20 substrate materials in dozens of etchant gas mixtures. These basic concepts can be used to select new etchants and plasma etching parameters.