A CCD based approach to high-precision size and refractive index determination of levitated microdroplets using Fraunhofer diffraction Rev.A simple method to determine the size of a spherical particle in an electrodynamic trap from its dynamic behavior is introduced. Contrary to common usage of electrodynamic traps, gravity is not compensated completely. The resulting oscillatory trajectory is phase shifted with respect to the driving ac field of the trap. A light barrier setup is sufficient to determine the phase lag. An analytical solution is available in closed form to yield the particle diameter from the measured phase lag. Numerical trajectory simulations support this solution. Our method is independent of the optical properties of the particle. Only the viscosity of the surrounding gas and the particle mass density have to be known for data evaluation.
The influence of the surface roughness of solid conducting spheres on the response of a phase‐Doppler anemometer (PDA) is described by using a ray theory model. A rough particle surface is modeled as an ensemble of distorted spheres. First‐ and second‐order reflection and diffraction are considered for far‐field calculations of the PDA phase difference. The numerical simulations are accompanied and supported by experimental results. Single rough Sn spheres are captured inside an electro‐dynamic trap and investigated with a standard phase‐Doppler system.
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