Real-time monitoring of vibration fringe patterns by optical reconstruction of digital holograms: mode beating detection
ABSTRACT A new technique capable of monitoring two-dimensional vibration fringe patterns in real-time is presented. It is based on optical reconstructing of time-averaged digital holograms. Recording of the holograms is realized in a quasi-Fourier off-axis setup whilst reconstructing in an extended Fourier transform setup capable of spatial filtering of the hologram reconstructions. The effectiveness of the proposed device, tested on a silicon wafer, was verified by performing operations such as monitoring of vibration modes, adjusting the hologram recording parameters, or searching for resonant frequencies. Additionally, mode beating between two distant vibration frequencies is observed and reported. The proposed technique is suitable for various scientific and industrial applications.
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ABSTRACT: The aim of this study was to (i) obtain the force-related interferometric patterns of loaded dental implant-abutment assemblies differing in diameter and brand using digital holographic interferometry (DHI) and (ii) determine the influence of implant diameter on the extent of load-induced implant deformation by quantifying and comparing the obtained interferometric data. Experiments included five implant brands (Ankylos, Astra Tech, blueSKY, MIS and Straumann), each represented by a narrow and a wide diameter implant connected to a corresponding abutment. A quasi-Fourier setup with a 25mW helium-neon laser was used for interferometric measurements in the cervical 5mm of the implants. Holograms were recorded in two conditions per measurement: a 10N preloaded and a measuring-force loaded assembly, resulting with an interferogram. This procedure was repeated throughout the whole process of incremental axial loading, from 20N to 120N. Each measurement series was repeated three times for each assembly, with complete dismantling of the implant-loading device in between. Additional software analyses calculated deformation data. Deformations were presented as mean values±standard deviations. Statistical analysis was performed using linear mixed effects modeling in R's lme4 package. Implants exhibited linear deformation patterns. The wide diameter group had lower mean deformation values than the narrow diameter group. The diameter significantly affected the deformation throughout loading sessions. This study gained in vitro implant performance data, compared the deformations in implant bodies and numerically stated the biomechanical benefits of wider diameter implants.Dental materials: official publication of the Academy of Dental Materials 01/2014; DOI:10.1016/j.dental.2013.12.005 · 4.16 Impact Factor
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ABSTRACT: This paper describes measurements of a vibrating object with rough surface by the time-averaged method of holography using a newly designed optically addressed liquid crystal spatial light modulator with a resolution of 102 lp/mm and a diffraction efficiency of 16%. An object vibrating faster than several tens of Hz could be visualized. The pattern obtained by the method provides the locus of vibrating nodes. The advantage of this method is that a high contrast pattern of a vibrating object can be imaged in near-real-time, although the sensitivity of vibration is decreased.Optics Communications 07/2007; 275(1):53-56. DOI:10.1016/j.optcom.2007.03.023 · 1.54 Impact Factor
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ABSTRACT: Corona discharges are generally characterized by a low optical density whose detection is often near or under the limits of interferometric techniques. In this paper, we propose a method of digital holographic interferometry that enables detection with enhanced sensitivity. This sensitivity increase is obtained by post-processing the digital holographic recordings with a set of point-wise image operations. The procedure is described mathematically and illustrated experimentally. Examples are given for an opaque object and for DC corona discharges generated in the symmetrical point-plane geometry.Optics Express 09/2007; 15(17):10672-80. DOI:10.1364/OE.15.010672 · 3.53 Impact Factor