München 2019 – scientific programme

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P: Fachverband Plasmaphysik

P 2: Complex and Dusty Plasmas I

P 2.5: Talk

Monday, March 18, 2019, 12:30–12:45, HS 20

High precision size measurement of microparticles during plasma operation — •Niklas Kohlmann, Frank Wieben, Oguz-Han Asnaz, Franko Greiner, and Dietmar Block — Kiel University, 24098 Kiel, Germany

Besides structural and dynamic processes in complex plasmas, the particles themselves are recently more and more in the focus of research. Important parameters are the particle size, shape and surface topology. However, non-invasive in-situ methods to determine the named parameters during plasma operation are missing. Angle-resolved Mie scattering measurements can fill this gap and provide particle sizes with high precision. An out-of-focus imaging technique similar to Interferometric Laser Imaging for Droplet Sizing (ILIDS) is used to obtain the angle-dependent scattering intensities. Correlating the measured data to those provided by the Lorenz-Mie theory for spherical objects, particle size and refractive index can be obtained. It is shown that the method allows to measure the particle size with an accuracy of a few nanometers if the polarization state of the laser light is taken into account. The particle size measurements are validated with complimentary measurements using a long distance microscope. It is found that the sizes are in good agreement for both methods. Further applications, like the detection of changes of particle surface topology due to plasma-particle interaction or the decrease in particle size due to prolonged plasma exposure, are discussed.