Feedback Control of Optically Trapped Particles

Abstract

Optical trapping is a method for manipulating micro- and nanoscale particles that are widely used in biophysics and colloid science, among other areas. This method uses optical forces to confine a particle to a localized region, which is referred to as a trap. This chapter examines the application of feedback control to optical trapping to improve particle localization, manipulation precision, and trap stability. Although control systems have been used in optical trapping for almost two decades, their perceived importance has largely been secondary to the scientific experiments that they support. As a result, only limited effort has been taken to explore the performance and stability of control systems in optical trapping. This chapter provides an introduction to the field and an overview of many of the issues relevant to a control systems perspective in optical trapping, including sensor and actuator performance, trap modeling, and instrument design. It also describes the design and implementation of a control system that has been used to dramatically improve the localization of a trapped particle with respect to the center of the trap. Many of the challenges in controlling optically trapped particles and future research directions for addressing these challenges are also described.