Robust laser beam tracking control using micro/nano dual-stage manipulators

This paper presents a study of the control problem of a laser beam illuminating and focusing a microobject subjected to dynamic disturbances using light intensity for feedback only. The main idea is to guide and track the beam with a hybrid micro/nanomanipulator which is driven by a control signal generated by processing the beam intensity sensed by a four-quadrant photodiode. Since the pointing location of the beam depends on real-time control issues related to temperature variation, vibrations, output intensity control, and collimation of the light output, the 2D beam location to the photodiode sensor measurement output is estimated in realtime. We use the Kalman filter (KF) algorithm for estimating the state of the linear system necessary for implementing the proposed track-following control approach. To do so a robust master/slave control strategy for micro/nano dual-stage manipulators is presented based on sensitivity function decoupling design methodology. The decoupled feedback controller is synthesized and implemented in a 6 dof micro/nanomanipulator capable of nanometer resolution through several hundreds micrometer range. A case study relevant to tracking a laser-beam for imaging purposes is presented.