Towards adaptive high-power lasers: Model-based control and disturbance compensation using moving horizon estimators

Abstract

Thermally-induced disturbances limit the beam quality of high-power lasers and evoke set point-dependent disturbances. As a result, the beam parameters and the laser’s output power of conventional high-power lasers cannot be chosen independently. To overcome this issue, we suggest spherical intra-cavity mirrors as actuators to dynamically compensate the impact of thermal lensing within the framework of automatic control. While the optical system is represented stationary as a Gaussian cavity with multiple transverse modes, the disturbance and the actuator are dynamically modeled by distributed parameters systems. A reliable estimation and prediction of the disturbance is crucial to achieve a proper rejection. To this end, an optimization-based moving horizon state estimator is designed to cope with model uncertainties, noisy measurements and bifurcations causing parasitic solutions of the nonlinear output equation. To maintain real-time capability, the relevant transient effects are lumped to an efficient discrete-time design model. The proposed compensation strategy explicitly considers input constraints and involves a reference governor to ensure the feasibility of the control objective. The performance of the individual components of the controller are validated by means of simulations and experiments. Eventually, we prove the overall concept of controlled adaptive high-power lasers by means of a scalable experimental setup with output lasers powers exceeding 500W.