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First-order nonconservative motion of optically trapped nonspherical particles
Stephen H Simpson1, Simon Hanna
1H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|January 15, 2011
Summary
Nonconservative optical forces cause cyclic motion in nonspherical particles trapped in optical fields. This first-order effect, unlike second-order effects in spheres, is not suppressed by increased beam power, impacting particle dynamics.
Area of Science:
- Optics
- Soft Matter Physics
- Statistical Mechanics
Background:
- Optical force fields are inherently nonconservative, influencing the thermal motion of trapped dielectric spheres.
- Spheres in optical traps do not reach thermodynamic equilibrium, achieving a steady state with biased cyclic motion.
- These effects are typically second-order and observed at low trap powers for spherical particles.
Purpose of the Study:
- To analyze the first-order nonconservative behavior of nonspherical particles in optical traps.
- To investigate how nonconservative forces affect particles with less than spherical symmetry.
- To understand the dependence of these effects on optical trap parameters.
Main Methods:
- Performing optical force calculations for nonspherical particles.
- Conducting Brownian dynamics simulations.
- Analyzing dielectric microrods held vertically in Gaussian optical traps.
Main Results:
- Nonspherical particles exhibit first-order nonconservative behavior in optical traps.
- This behavior is dependent on the linear term in the optical force field.
- Increased beam power does not suppress these first-order effects, though it influences cyclic motion frequency and amplitude.
Conclusions:
- First-order nonconservative effects are significant for nonspherical particles in optical traps.
- Unlike spherical particles, these effects are not diminished by higher laser power.
- The study provides insights into the dynamics of anisotropic particles in optical fields, relevant for micro-manipulation and fundamental physics.
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