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Abstract <p>Double-exposure laser speckle photography is an extensively used technique for measuring in-plane displacements in experimental mechanics. Double-exposure specklegrams recorded using this technique give speckle correlation fringes of Young’s type in a diffraction halo when illuminated with an unexpanded beam of laser light. In-plane displacement is measured by measuring the width of these fringes. However, due to diffraction halo intensity, the minima of speckle correlation fringes move away from the center, and the maxima come closer to the center. This decreases the accuracy of the measurement of fringe width and leads to errors in the in-plane displacement measurement. To get rid of the effect of diffraction halo on the measurement of widths of speckle correlation fringes, several researchers have done considerable work for the necessary corrections in the measured value of fringe widths. Further, the double-exposure specklegrams record the vector displacement of a point, and the corresponding Young’s fringes are always orthogonal to the in-plane displacement. Thus, to measure the in-plane displacement components accurately, one has to accurately measure the orientation θ of these fringes with x and y directions. Any inaccuracies in measuring θ may lead to significant errors in the measurement of in-plane displacement components. To eliminate these errors in the measurement of width of speckle correlation fringes, we present an experimental technique for the measurement of the in-plane displacement component in speckle photography, where we have used two identical holographic lenses with dual apertures and data regarding the fringe spacing have been obtained from ± first diffracted orders. Experiments have been performed using suitably designed holographic lenses. In-plane displacements given to a diffuse object have been measured using the experimental method proposed in this work. The obtained results are in good agreement with the results reported with the necessary corrections in fringe width in the literature. This confirms the validity of the proposed method.</p>

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An Experimental Method to Minimize Errors in the In-Plane Displacement Measurements in Laser Speckle Photography Using a Dual Aperture Compact HoloLens Imaging System

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • Rajendra Kumar Jayaswal,
  • Arasad Ali Khan,
  • Hira Lal Yadav

摘要

Abstract

Double-exposure laser speckle photography is an extensively used technique for measuring in-plane displacements in experimental mechanics. Double-exposure specklegrams recorded using this technique give speckle correlation fringes of Young’s type in a diffraction halo when illuminated with an unexpanded beam of laser light. In-plane displacement is measured by measuring the width of these fringes. However, due to diffraction halo intensity, the minima of speckle correlation fringes move away from the center, and the maxima come closer to the center. This decreases the accuracy of the measurement of fringe width and leads to errors in the in-plane displacement measurement. To get rid of the effect of diffraction halo on the measurement of widths of speckle correlation fringes, several researchers have done considerable work for the necessary corrections in the measured value of fringe widths. Further, the double-exposure specklegrams record the vector displacement of a point, and the corresponding Young’s fringes are always orthogonal to the in-plane displacement. Thus, to measure the in-plane displacement components accurately, one has to accurately measure the orientation θ of these fringes with x and y directions. Any inaccuracies in measuring θ may lead to significant errors in the measurement of in-plane displacement components. To eliminate these errors in the measurement of width of speckle correlation fringes, we present an experimental technique for the measurement of the in-plane displacement component in speckle photography, where we have used two identical holographic lenses with dual apertures and data regarding the fringe spacing have been obtained from ± first diffracted orders. Experiments have been performed using suitably designed holographic lenses. In-plane displacements given to a diffuse object have been measured using the experimental method proposed in this work. The obtained results are in good agreement with the results reported with the necessary corrections in fringe width in the literature. This confirms the validity of the proposed method.