Many studies to determine the parameters of rough surfaces by optical methods were made. Some of them are related to the problem of surfaces immersed in a liquid, making the assumption of the equivalence between the surface immersed and other surface with an "apparent roughness". This paper deal with this kind of problems making a theoretical study of the light scattered by a very rough reflecting surface, σ >> λ, and the light scattered by the same surface immersed in a liquid of refractive index n. The general Kirchhoff solution for scattering from a rough surface is used. This work shows that under certain conditions the mean scattered intensity from a surface immersed in a liquid can be quasi-indistinguishable from another surface not immersed, called "apparent surface".
A theoretical model describing speckle correlation as a decreasing quadratic exponential function of roughness changes was published in a previous paper. In this work, the theoretical model in a real situation is analyzed: paint drying over rough surfaces with a roughness larger than the wavelength of the He-Ne laser beam used to illuminate it. Speckle correlation of the scattered light is applied to study changes in the system surface-drying paint.
A digital algorithm is used to evaluate the correlation of speckles taken while the paint dries. The speckle patterns are captured at different moments of the process, i.e., a first set of pictures when the paint is fresh (first 30 minutes) and another set in a period of several hours. The speckle patterns in the early group were stored every one or two minutes. The speckle correlation is evaluated between the first picture and the others. A graph of correlation vs. time is analyzed using the model and considering that the solvent evaporation follows a decreasing exponential function.
The other group is formed by speckle patterns stored every twenty minutes. The speckle patterns are studied as mentioned above and the correlation between one picture and the next is performed as well. That is, the speckle correlation is now evaluated between consecutive patterns. These experimental changes are compared with the theoretical model. Good agreement between the theoretical and experimental results is found.
New results obtained with the method to measure the refractive index in liquids by using a speckle pattern are presented.
When a laser beam impinges obliquely on a transparent rectangular cell, its direction of propagation undergoes a lateral shift when the cell is filled with a liquid. The shift depends only on the refractive index of the liquid, on the distance between the parallel walls of the cell and on the incident angle. Similarly, if the cell is illuminated by a speckle pattern, the latter suffers a displacement when the liquid is introduced. A CCD camera records the transmitted speckle pattern before and after filling of the cell with the liquid.
The images are stored in a PC and processed with software to obtain the refractive index. The advantage in determining the displacement through the use of a speckle pattern is that a sub pixel processing can be made of the shifting caused by the liquid. The refractive indices of some liquids were performed, with errors under 1%: acetone, alcohol, water, xylene, butanol, dilution of butanol in xylene and a saturated solution of salt in water.
This work studies rough surfaces that undergo small random morphological changes. In the present paper, rough reflective surfaces are dealt with. Its roughness is larger than the wavelength of the He-Ne laser beam used to illuminate it. Speckle correlation of the scattered light is applied to study changes in the roughness.
A theoretical model, which describes speckle correlation as a decreasing quadratic exponential function of roughness changes and was presented in a previous paper, is used.
New experimental results from rough reflective surfaces in which the changes are simulated through immersion of the samples in liquids with different refraction indices are presented.
Good agreement between the theoretical and experimental results is found.
The study of light scattered from changing surfaces (oxidation, erosion, etc.) is of great interest because of its application in aging control of mechanical components. The models presented in this paper are the results of Optics and Laser Lab. studies of rough surfaces by means of light scattering. First, a model for studying the electroerosion process, as a particular case of pitting corrosion, is presented. Second, another model for studying random changes in roughness surface is also presented. The theoretical results are compared with those obtained experimentally. In summary, it is shown that statistics properties of the light scattered by this kind of surfaces can be taken into account as a parameter to analyze these morphological changes.
The study of light scattered from changing surfaces is of great interest because of its application in aging control of mechanical components and other problems. In many situations it is important to know the roughness changes in dielectric or metallic surfaces. Often, this roughness variation must be determined in a non-destructive way. In this work it is reported some new results related with the study of roughness variations. In recent works were presented some aspects of a developed theoretical model that relates the speckle correlation with changes in the surface roughness. This model is valid for dielectric or metallic surfaces, however, for the sake of simplicity, it is studied a translucent diffuser. It is recorded the transmitted speckle pattern for a translucent rough surface before and after it suffers a change, and then it is calculate the correlation between both speckle patterns. The roughness is changed in a controlled way by means of immersion liquids of different refractive indices. A good agreement between the theoretical description and experimental results obtained in quasi-real time is achieved.
This work describes the application of mean intensity diffusion analysis to detect and analyze metallic corrosion phenomena. We present some new results in the characterization of the corrosion process using a model based in electroerosion phenomena. Valuable information is provided about surface microrelief changes, which is also useful for numerous engineering applications. The quality of our results supports the idea that this technique can contribute to a better analysis of corrosion processes, in particular in real time.
This paper describes the use of optical correlation speckle patterns to detect and analyze the metallic corrosion phenomena, and shows the experimental set-up used. We present some new results in the characterization of the corrosion process using a model based in electroerosion phenomena. We also provide valuable information about surface microrelief changes, which is also useful in numerous engineering applications. The results obtained are good enough for showing that our technique is very useful for giving new possibilities to the analysis of the corrosion and oxidation process, particularly in real time.
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