Mapping the restoring force of an optical trap in three dimensions using a two laser dual-trap approach

A two laser optical tweezers set-up is developed and used to measure deflections of a microsphere trapped in a calibrated spatial light modulator steered probe trap as it is stepped through a three dimensional grid about a fixed test trap. These measurements are used to map the restoring force of the test trap on the microsphere in three dimensions. Results are validated over a common range by comparison to drag force measurements for both silica and polystyrene microspheres.