Issue
EPL
Volume 81, Number 5, March 2008
Article Number 58005
Number of page(s) 5
Section Interdisciplinary Physics and Related Areas of Science and Technology
DOI http://dx.doi.org/10.1209/0295-5075/81/58005
Published online 19 February 2008
EPL, 81 (2008) 58005
DOI: 10.1209/0295-5075/81/58005

Multiple trapped states and angular Kramers hopping of complex dielectric shapes in a simple optical trap

J. N. Wilking1 and T. G. Mason1, 2, 3

1  Department of Chemistry and Biochemistry, University of California-Los Angeles - Los Angeles, CA 90095, USA
2  Department of Physics and Astronomy, University of California-Los Angeles - Los Angeles, CA 90095, USA
3  California NanoSystems Institute, University of California-Los Angeles - Los Angeles, CA 90095, USA

mason@physics.ucla.edu

received 7 October 2007; accepted in final form 16 January 2008; published March 2008
published online 19 February 2008

Abstract
Custom-shaped dielectric colloids in a simple focused laser beam create complex multi-dimensional potential landscapes. For laser powers above the threshold needed to trap spheres, many intricate shapes having holes and arms, as sampled using letters that have thicknesses comparable to the wavelength, can be trapped stably in more than one position and orientation. Particular trapped states can be reproducibly obtained by controlling how a particle enters the trap. By systematically enlarging the central hole of a square toroid, we alter the location, orientation, and existence of a trapped state. Thermal fluctuations of the trapped letter "N" cause Kramers hopping between two preferred orientational states, yielding a double-well angular potential.

PACS
82.70.Dd - Colloids.
87.80.Cc - Optical trapping.
05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.

© EPLA 2008