10 June 2006 Diffraction-shadow technique of single bubble size and velocity measurements
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Proceedings Volume 6262, Optical Methods of Flow Investigation; 62620H (2006) https://doi.org/10.1117/12.683022
Event: Optical Methods of Flow Investigation, 2005, Moscow, Russian Federation
Abstract
The purpose of the work is the theoretically and experimentally investigation of Gaussian laser beam diffraction by a single particle or gas bubble moving in a liquid. The size of the bubble or particle is assumed to be comparable with the radius of the beam. The results of this investigation are applied to develop and implement the technique for simultaneous measurements of the bubble or particle radius and velocity. It is shown that the field diffracted by a bubble exceeds the refracted and reflected fields in the beam propagation direction. The diffracted field is simulated using the scattering theory for a spherical particle based on the Kirchhoff approach. In addition to scattering on bubbles or spherical particles diffraction by a moving cylindrical particle is analyzed. An experimental setup has been designed to verify the theoretical background of the technique. The fields radiated by the central part of the laser beam and scattered by a particle or bubble in the forward direction are incident on the photo detector placed at the center of the observation plane. As a bubble or particle moves, the diffraction pattern (diffraction shadow) shifts over the observation plane. This results in variations of the photo detector output current. It is shown that the radius of the laser beam that is optimum for measurements should be approximately equal to the radius of the first Fresnel zone. Based on the research results, recommendations for the choice of the setup parameters and for determination of the measurement error are given.
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B. S. Rinkevichyus, I. L. Raskovskaya, A. V. Tolkachev, "Diffraction-shadow technique of single bubble size and velocity measurements", Proc. SPIE 6262, Optical Methods of Flow Investigation, 62620H (10 June 2006); doi: 10.1117/12.683022; https://doi.org/10.1117/12.683022
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