کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5428705 | 1508689 | 2013 | 8 صفحه PDF | دانلود رایگان |
Radiation pressure forces from a moderately focused vertical laser beam are used to levitate transparent particles, a few micrometers in size. Having recalled basic results about levitation of spheres, and applications to long-working distance trapping, we turn to ellipsoid-shaped particles. Experiments are carried out with polystyrene particles, inside a glass chamber filled with water. The particles are lifted up to contact with the chamber top surface. We examine particle equilibrium in such conditions and show that the system “bifurcates” between static on-axis equilibrium with short ellipsoids, to sustained oscillations with longer ones. A similar Hopf bifurcation is found using a simple ray-optics model of the laser-ellipsoid interaction, providing a qualitative account of the observed oscillations.
⺠We study optical levitation of non-spherical micrometer-sized particles. ⺠Short ellipsoids get trapped on laser beam axis, similarly to spheres. ⺠Long ellipsoids oscillate, through coupled translation and tilt motions. ⺠We propose a simple ray-optics model of light interaction with an ellipsoid. ⺠From computed radiation pressure forces, we explain the observed oscillations.
Journal: Journal of Quantitative Spectroscopy and Radiative Transfer - Volume 126, September 2013, Pages 61-68