Didactic laser speckle experiments with a lensless camera

Fujiwara, Eric; Fracarolli, Juliana Aparecida; Cordeiro, Cristiano M. B.

doi:10.1088/1361-6404/ac2b04

Cited by 8 publications

(3 citation statements)

References 16 publications

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“…Papers using laser speckle with didactic purposes have been published, e.g. [1][2][3][4][5]. However, the authors of the present work have not found educational papers reporting speckle techniques related to vibrations.…”

Section: Introductionmentioning

confidence: 86%

Speckle interference for naked-eye detection of vibrations

Córdova,

Limón,

Torres

2024

Eur. J. Phys.

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An affordable optical project for students is explained in this work. The experiment only requires a handheld laser illuminating a structure with stationary vibrations induced, but the interpretation of this phenomenon demands a strong understanding of optical interference and modal behavior of a bar. The operating principle employs the speckle phenomenon, which is a type of interference between coherent light incident on a rough surface and its reflection. This interference occurs in a luminous plane outside of the vibrating object and shows a granular structure due to the brightness fluctuations. Speckle is static but if the surface illuminated oscillates, the plane of interference moves from one side to the other, causing a streak pattern. Mode shapes of the object under examination can be naked eye detected from streak patterns. What is more, this phenomenon can be photographed using a manual focus digital camera. Therefore all the components of the procedure can be available (or acquired) by almost any physics laboratory, at any level, which would be unthinkable for optical experiments just a few years ago.

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Section: Introductionmentioning

confidence: 86%

Speckle interference for naked-eye detection of vibrations

Córdova,

Limón,

Torres

2024

Eur. J. Phys.

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“…The tests proceeded at room temperature, with environmental illumination absent and the setup mounted on a vibration‐free breadboard. The optical system and camera parameters are carefully adjusted to avoid saturation and improve the speckles contrast 19 . The algorithm evaluates both ZNCC and EZNCC (threshold empirically set as τ = 0.5) for the sake of comparison, yielding quantitative results regarding sensitivity, resolution, and dynamic range.…”

Section: Methodsmentioning

confidence: 99%

Enhancing the measurement range of laser speckle systems

Cabral

Cordeiro

Fujiwara

2022

Micro & Optical Tech Letters

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Laser speckle-based systems provide sensitive measurements of displacement and stain. However, the typical saturation of correlation functions restricts the application of such techniques regarding their dynamic range. Therefore, this paper proposes using the extended zero-mean normalized cross-correlation (EZNCC) algorithm to automatically update the reference speckle image according to a programmable threshold, allowing for exceeding the decorrelation limit. Experiments investigated the effect of rigid body displacements and thermal strain at the light scattering surface (a ceramic container). The EZNCC yielded ~30 μm resolution over a continuous 1500 μm range for displacement measurements, and ~0.2°C resolution between 21.5°C and 61.5°C for the temperature analysis. As this method requires minor updates to the traditional correlation algorithms, the ENZCC does not require modifications to the optical setups, improving the dynamic range and ensuring the high sensitivity of speckle correlation systems in a feasible, straightforward approach.

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“…The size of this single speckle in the detector plane depends on the design of the experiment, particularly if we use or not a lens at the detector. For our measurements, we use a lens-less system, hence the size of a single speckle is equal to [146].…”

Section: Enhancement In Presence Of Variable Speckle Sizementioning

confidence: 99%

Transparency, Secrecy, and Profiling Using Mutual Scattering in Complex Media

Rates

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DISSERTATIONto obtain the degree of doctor at the University of Twente, on the authority of the rector magnificus, prof.dr.ir. A. Veldkamp, on account of the decision of the Doctorate Board, to be publicly defended on Tuesday the 10 th of October 2023 at 14.45 by Alfredo Rates Soriano born on the 2 nd of February 1995 in Santiago, Chile. This dissertation has been approved by: Promotors: prof.dr. W.L. Vos prof.dr. A. Lagendijk Cover: Cover inspired by classic book covers. The symbols at the corners represent the random walk made by light in a scattering medium, while the square grids on the sides represent the segments of light modulation. On the back, three symbols appear representing the three projects of the thesis: mutual scattering to control transparency (top), physical unclonable functions (bottom left), and wavefront modulation to characterize objects (bottom right). Concept by Alfredo Rates and design by Paula García Miranda

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Didactic laser speckle experiments with a lensless camera

Cited by 8 publications

References 16 publications

Speckle interference for naked-eye detection of vibrations

Speckle interference for naked-eye detection of vibrations

Enhancing the measurement range of laser speckle systems

Transparency, Secrecy, and Profiling Using Mutual Scattering in Complex Media

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