Optically trapped microshperes can be manipulated by steering the trap beam, while the object position is measured with sub-nanometer resolution. A fast steering system is required to create feedback loop for measurements at a constant force or to increase position detection precision by trap stiffening. Using a real-time re-programmable digital signal processor, we combine steering and position detection to create a fast and versatile closed-loop feedback controlled instrument. We describe the construction and calibration of the instrument. We show that a proportional gain position-clamp algorithm can achieve about 10-fold increase in effective trap stiffness while higher gains lead to unwanted resonances.
|Series||Proceedings of SPIE|