Three-dimensional measurement of the local extinction coefficient in a dense spray

Abstract:
Laser extinction, signal attenuation and multiple scattering are the three main phenomena limiting qualitative and quantitative measurements in planar laser imaging of sprays. In this paper, a method is presented where structured laser illumination planar imaging is used to remove the signal contribution from multiply scattered light. Based on this technique, data from side scattering and transmission measurements are obtained simultaneously. An algorithm, compensating for signal attenuation and laser extinction, is further applied to calculate the local extinction coefficient. The method is first demonstrated on a cuvette containing a homogeneous solution of scattering particles with an extinction coefficient (mu) over bar (e) = 0.13 mm(-1). Finally the procedure is applied on an air-assisted water spray with a maximum optical depth of OD similar to 3, where the position-dependent extinction coefficient is extracted within the probed volume. To the best of our knowledge, this paper demonstrates for the first time a method to measure the local (mu) over bar (e) within the three dimensions of an inhomogeneous scattering medium using laser sheet illumination, after suppression of the multiple light scattering intensity.