Optical forces, trapping and strain on extended dielectric objects

¹ Institute for Theoretical Physics, University of Innsbruck - Technikerstraß e 25, A-6020 Innsbruck, Austria, EU
² Division for Biomedical Physics, Innsbruck Medical University - Müllerstraß e 44, A-6020 Innsbruck, Austria, EU

^a Matthias.Sonnleitner@uibk.ac.at

Received: 3 February 2011
Accepted: 31 March 2011

Abstract

We show that the optical properties of an extended dielectric object are reliably reproduced by a large number of thin slices forming a linear array of beam splitters. In the infinite slice number limit this self-consistent approach allows to calculate light forces within a medium directly from the Maxwell stress tensor for any dielectric with prescribed refractive index distribution. For the generic example of a thick slab in counterpropagating fields the effective force and internal strain distribution strongly depend on the object's thickness and the injected field amplitudes. The corresponding trapping dynamics may even change from high-field-seeking to low-field-seeking behaviour while internal forces lead to pressure gradients and thus imply stretching or compression of an elastic object. Our results bear important consequences for a wide scope of applications, ranging from cavity optomechanics with membranes, size selective optical trapping and stretching of biological objects, light-induced pressure gradients in gases, to implementing light control in microfluidic devices.