Accounting for multiple scattering, signal attenuation and laser extinction using Structured Laser Illumination Planar Imaging

In planar laser imaging of optically dense sprays, artifacts from laser extinction and signal attenuation can only be removed if effects introduced by multiple scattering are suppressed beforehand. In this article Structured Laser Illumination Planar Imaging (SLIPI) is used to simultaneously account for multiple light scattering, monitor the incident laser power and estimate the true light transmission. By applying this novel approach and recording data at successive depths within an atomizing spray, light losses due to laser extinction and signal attenuation could be compensated for by post-processing calculations based on the Beer-Lambert law. Finally an estimation of the local extinction coefficient is extracted within the three dimensions of an inhomogeneous cloud of droplets. In this investigation an aerated water spray running at 3 bar water and 4.2 bar air injection pressure is used. Due to the internally air-assisted design of the nozzle, an optically dense cloud of fine droplets was generated with a minimum of 5 % light transmission at 2.3 cm below the nozzle tip. It is believed that this new method, which account for laser extinction and signal attenuation after the initial correction of multiple scattering by means of SLIPI, is key to extract and reconstruct a correct representation of the extinction coefficient within an inhomogeneous cloud of polydisperse droplets. Such quantitative information is of fundamental importance for advanced analysis, optimization and control of modern atomizing sprays.