Abstract

Multiple microscopic particles in liquid suspension trapped in a laser beam mutually interact through their scattered field components. Overall, they are subject to several forces: radiation pressure, field gradient (used for optical tweezers) and scattered field. The latter is a strongly nonlinear function of the relative positions, since the field rapidly oscillates in space around the scatterer and decays slowly with distance. This interaction lies at the core of the well-known difficulty in freely manipulating pairs of particles with optical tweezers, whereby the problem is technically solved by using non-interfering laser fields for the different particles (by appropriate polarization or wavelength selection). Although this interaction has been identified long ago in experiments involving optical manipulation of microspheres [1], little work has been dedicated to its detailed investigation.

© 2007 IEEE