Design and Characterization of Four-Degree-of-Freedom Fast Steering Mirror for Laser Compensation System

The accuracy and stability of laser are influenced not only by external environmental factors but also by the laser internal structure, heat source, input source, etc., resulting in four-degree-of-freedom (4-DOF) laser disturbances. In this study, to reduce the laser disturbances and improve laser quality, a 4-DOF fast steering mirror (FSM) with double Porro prisms, which is driven by a voice coil motor (VCM), was designed for a laser compensation system. The 4-DOF FSM addressed the limitations of commercial laser compensation systems by achieving a shorter optical path length, reducing the number of components, and simplifying the setup of laser compensation systems at various positions. Furthermore, it enhanced the static and dynamic performance of a 4-DOF FSM proposed in a previous study. Finite element analysis was conducted to analyze both the electromagnetic structure and mechanical structure of the proposed 4-DOF FSM. Furthermore, a mathematical model was established for its motion dynamics, ensuring that its static and dynamic performance satisfied the conditions of compensating laser disturbances. Finally, a PID closed-loop control was established for the 4-DOF FSM laser compensation system. By comparing the differences before and after laser compensation using the 4-DOF FSM, the compensatory function of the 4-DOF laser compensation system was validated, achieving real-time compensation for laser disturbances.