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

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

Corresponding author: mason@physics.ucla.edu

Received: 7 October 2007
Accepted: 16 January 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.