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Proceedings Paper

Generalized Lorentz Law and the force of radiation on magnetic dielectrics
Author(s): Masud Mansuripur
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Paper Abstract

The macroscopic equations of Maxwell combined with a generalized form of the Lorentz law are a complete and consistent set; not only are these five equations fully compatible with the special theory of relativity, they also conform with the conservation laws of energy, momentum, and angular momentum. The linear momentum density associated with the electromagnetic field is ΡEM(r,t)=E(r,t)×H(r,t)/c2, whether the field is in vacuum or in a ponderable medium. [Homogeneous, linear, isotropic media are typically specified by their electric and magnetic permeabilities εο ε(ω) and μομ(ω).] The electromagnetic momentum residing in a ponderable medium is often referred to as Abraham momentum. When an electromagnetic wave enters a medium, say, from the free space, it brings in Abraham momentum at a rate determined by the density distribution ΡEM(r,t), which spreads within the medium with the light's group velocity. The balance of the incident, reflected, and transmitted (electromagnetic) momenta is subsequently transferred to the medium as mechanical force in accordance with Newton's second law. The mechanical force of the radiation field on the medium may also be calculated by a straightforward application of the generalized form of the Lorentz law. The fact that these two methods of force calculation yield identical results is the basis of our claim that the equations of electrodynamics (Maxwell + Lorentz) comply with the momentum conservation law. When applying the Lorentz law, one must take care to properly account for the effects of material dispersion and absorption, discontinuities at material boundaries, and finite beam dimensions. This paper demonstrates some of the issues involved in such calculations of the electromagnetic force in magnetic dielectric media.

Paper Details

Date Published: 29 August 2008
PDF: 10 pages
Proc. SPIE 7038, Optical Trapping and Optical Micromanipulation V, 70381T (29 August 2008); doi: 10.1117/12.796530
Show Author Affiliations
Masud Mansuripur, College of Optical Sciences, The Univ. of Arizona (United States)


Published in SPIE Proceedings Vol. 7038:
Optical Trapping and Optical Micromanipulation V
Kishan Dholakia; Gabriel C. Spalding, Editor(s)

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