We present a few simple examples to illustrate certain fundamental properties of the EM field. Using elementary physical concepts, we explain the nature of interactions that involve exchanges of energy, linear momentum, and angular momentum between EM fields and material media. First, the radiation force experienced by a small, polarizable particle which has a predetermined dielectric susceptibility will be examined. The dielectric susceptibility of small spherical particles will be related to their refractive index (with proper accounting for the effects of radiation resistance). We describe the relation between the energy and orbital angular momentum of a cylindrical harmonic EM wave trapped inside a hollow cylindrical cavity, and explore the relations among the energy, linear momentum, and angular momentum picked up by a small particle under illumination by a cylindrical harmonic EM wave. In light of this analysis, it becomes clear why a small particle spins around its own axis when illuminated by a light beam that carries spin angular momentum, whereas the same particle tends to orbit around an axis of vorticity when exposed to a beam (such as a vector cylindrical harmonic) that possesses orbital angular momentum.
Masud Mansuripur, "Angular momentum exchange between light and small particles (Conference Presentation)," Proc. SPIE 10347, Optical Trapping and Optical Micromanipulation XIV, 1034710 (Presented at SPIE Nanoscience + Engineering: August 07, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2273225.5581152002001.
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