Material Property / State Characterization by Laser Speckle Photometry (original) (raw)
Related papers
Displacement Measurement and Study of Surface Roughness using Laser Speckle Technique
A simple technique of speckle photography has been applied to measure small changes/deformation of the surface of laser scattering materials. Low-cost commercial charge coupled device photo camera provides the images of Laser speckle pattern with the beam splitter arrangement. A speckle pattern has been taken with the system at rest and then second image captured after the deformation was made in the surface of the material. By simple subtraction of the two images, gives information about displacement by means of correlation fringes. Binary speckles are used to study surface roughness and compared with stylus profilometer method.
Applied Mechanics and Materials, 2010
Strain field measurement with non intrusive techniques is needed in order to characterize the behaviour of steels at high temperatures subjected to small displacements. In this work we present a technique based on laser-produced speckles coupled with a cross-correlation cross-spectrum method. This method proves more accurate than cross-correlation for small displacements. The laser wave length used (532 nm) allows to perform strain measurements, even with heat radiation.
NON DESTRUCTIVE FLAW DETECTION BY LASER SPECKLE PHOTOGRAPHY
Laser Speckle Photography, a non destructive optical method is presented to study the defect of a metal surface with the help of image processing technique. The speckle effect is due to the self-interference of coherent light source of He-Ne laser incident on an optically rough surface. This method is employed to identify the flaws by examining the induced strain concentration due to deformation. The fringe pattern is obtained and the defect can be analyzed by Fast Fourier transform.
2017
Optical Non-Destructive Evaluation (NDE) based on laser speckle techniques is gaining mor e popularity in recent years due to their ability to effectively quantify and qualify potential fla ws. Laser speckle can be inferred as a random pattern of interference that is explained with statistical methods. As the s peckle pattern is produced by the superposition of many wave fronts with random phases, scattered fr om different parts of the rough surface, its dependence with statistical indices may provide a more sharp estimation of speck le fluctuations. The present study illustrates two statistical tools, such as entropy and Principal Component Analy sis (PCA) for defining statistical properties of speckle intensity variations. Since entropy being a measure of randomness of speckle intensity variations, it is used in this study to characterize the statistical nature of the speckle pattern as a function of surface roughness of the object. The entropy analysis of four samples wit h diffe...
Different methods for characterizing surface roughness using laser speckle technique
Iraqi Journal of Physics, 2019
In this work, results from an optical technique (laser speckle technique) for measuring surface roughness was done by using statistical properties of speckle pattern from the point of view of computer image texture analysis. Four calibration relationships were used to cover wide range of measurement with the same laser speckle technique. The first one is based on intensity contrast of the speckle, the second is based on analysis of speckle binary image, the third is on size of speckle pattern spot, and the latest one is based on characterization of the energy feature of the gray level co-occurrence matrices for the speckle pattern. By these calibration relationships surface roughness of an object surface can be evaluated within these relations ranges from single speckle pattern image which was taken from the surface.