Oral presentation at the 15th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal.
At the 15th International Symposium on Applications of Laser Techniques to Fluid Mechanics, held from July 5–8, 2010, in Lisbon, Portugal, an oral presentation was given on the determination of the size and refractive index of a single water droplet using a light source with short coherence length. The contribution demonstrated an advanced optical approach for precise single-droplet characterization in fluid-mechanical applications.
Determination of Size and Refractive Index of a Single Water Droplet by Using a Light Source with Short Coherence Length
Abstract
The use of short coherence length light sources for optical particle characterization offers a number of interesting features, whose potential have not yet been fully explored or exploited. For one, such light sources can be considerably less expensive than lasers, with particular reference to high-intensity and highly durable LEDs (light emitting diodes). Furthermore, as with femtosecond light sources, the short coherence length suppresses interference between various scattering orders in the far field, leading to a more monotonic intensity dependence as a function of particle size. The lack of polarization can contribute in the same manner to a reduction of interference phenomena. This can be especially attractive if intensity or intensity ratio measures are to be used in estimating particle characteristics. What is not clear is which measurement principles can best exploit these features.
The present work investigates the use of glare point imaging for estimating size and refractive index of spherical, transparent particles/droplets. Two measures are used to determine these two quantities, the separation between the reflective and 2nd order refractive glare points, and the intensity ratio between the two. A velocity measurement is not considered, but could be easily implemented using a time-of-flight measurement through two illuminating sheets or by multiple imaging and a particle tracking approach.