Development of a new velocity measurement technique : the laser bessel velocimetry

Abstract

The present thesis describes the design, construction and testing of a new velocity measurement optical technique system. The technique has similarities with the laser Doppler velocimetry (LDV) in that it uses scattered light detection, in order to measure one component of the velocity vector of moving flows or solid surfaces. It uses the fringes of a Bessel beam produced by an axicon to generate the measurement volume. This technique, which we call Laser Bessel velocimetry (LBV), is noninvasive and permits continuous velocity measurements of moving particles. The experimental measurement set-up including the laser source, the optical devices, a moving stage with known velocities, a photodetector to capture scattered light and signal processing and data acquisition components, was developed and used to provide a proof of concept of this new technique. The set-up was also tested with a commercial LDV system. Two types of refractive linear axicons have been used to generate a Bessel type beam by illuminating the axicons with blue and red collimated and coherent laser light of dissimilar wavelengths, λ. The linear axicons offer the advantage of simplicity. The software tools for measurements, acquisition and analysis of the data are developed using NI Labview and MATLAB. Results from both theoretical simulation and experimental measurements are presented and compared.