Appropriate Laser Focusing Configuration for Number Density Measurement of Water Droplets in an Aerosol by Laser-Induced Breakdown Method

概要

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The number density of water droplets in an aerosol can be experimentally evaluated by a laser-induced breakdown method with different focal configurations. The detection volume is evaluated from the intensity ratio between the breakdown threshold and the actual laser irradiation and focal parameters. The number of droplets in a volume is evaluated from the breakdown probability. The number density is determined by the experimentally observed detection volume and the number of droplets. Theoretical calculations indicate that an appropriate focus configuration in which breakdown is generated at a laser intensity over three times the breakdown threshold reduces the measurement error of the volume, and an appropriate breakdown probability reduces the sampling error due to the limited number of laser shots. These findings are consistent with the experimental results in terms of the difference in the measured number density with different focal configurations and the nonlinear increase of the number of droplets as a function of the volume. These results also indicate the appropriate detection range of the number density of droplets for a certain focus configuration and the accuracy of the experimental results.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2010-07-25