Radiation force on a nonlinear microsphere by a tightly focused Gaussian beam

College

College of Science

Department/Unit

Physics

Document Type

Article

Source Title

Applied Optics

Volume

41

Issue

36

First Page

7694

Last Page

7701

Publication Date

12-20-2002

Abstract

We determine the characteristics of the radiation force that is exerted on a nonresonant nonlinear (Kerr-effect) rigid microsphere by a strongly focused Gaussian beam when diffraction and interference effects are significant (sphere radius a ≤ illumination wavelength λ). The average force is calculated from the surface integral of the energy-momentum tensor consisting of incident, scattered, and internal electromagnetic field vectors, which are expressed as multipole spherical-wave expansions. The refractive index of a Kerr microsphere is proportional to the internal field intensity, which is computed iteratively by the Rytov approximation (residual error of solution, 10-30). The expansion coefficients for the field vectors are calculated from the approximated index value. Compared with that obtained in a dielectric (linear) microsphere in the same illumination conditions, we find that the force magnitude on the Kerr microsphere is larger and increases more rapidly with both a and the numerical aperture of the focusing objective. It also increases nonlinearly with the beam power unlike that of a linear sphere. The Kerr nonlinearity also leads to possible reversals of the force direction. The proposed technique is applicable to other types of weak optical nonlinearity. © 2002 Optical Society of America.

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Digitial Object Identifier (DOI)

10.1364/AO.41.007694

Disciplines

Physics

Keywords

Gaussian beams; Radiation

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