Fashioning microscopic tools

Abstract

By moulding optical fields, holographic optical tweezers are able to generate structured force fields with magni- tudes and length scales of great utility for experiments in soft matter and biological physics. Optically induced force fields are determined not only by the incident optical field, but by the shape and composition of the par- ticles involved. Indeed, there are desirable but simple attributes of a force field, such as rotational control, that cannot be introduced by sculpting optical fields alone. In this work we describe techniques for the fabrication, sample preparation, optical manipulation and position and orientation measurement of non-spherical particles. We demonstrate two potential applications: we show how the motion of a non-spherical optically trapped force probe can be used to infer interactions occurring at its tip, and we also demonstrate a structure designed to be controllably rotated about an axis perpendicular to the optical axis of the beam.