Theoretical determination of the radiation force for a spherical particle illuminated by a focused laser beam

Reto Dorizzi, Z. Ulanowski

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Abstract

Trapping forces on dielectric spheres in single beam laser tweezers are computed. A focused beam description based on an exact solution of Maxwell's equations is compared to the 5th order Gaussian beam approximation due to Barton and Alexander. Forces on water droplets suspended in air and on polystyrene spheres suspended in water, exerted by beams focused to varying degree, are calculated. It is demonstrated that the 5th order approximation is accurate for almost paraxial beams (numerical aperture NA <similar to 0.25), as compared to the exact treatment. However, for strongly focused beams the 5th order approximation breaks down. Thus it is established that an accurate beam description is vital for modeling optical traps, since, in order to hold a particle effectively in a single beam trap, a strongly focused beam is required. (C) 2009 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)1483-1489
Number of pages7
JournalJournal of Quantitative Spectroscopy and Radiative Transfer
Volume110
Issue number14-16
DOIs
Publication statusPublished - 2009

Keywords

  • Gaussian laser beam
  • non-paraxial beam
  • optical trapping force
  • laser tweezers
  • optical trapping

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