On Compensating Thermal Lensing in High-Power Lasers Using Intra-Cavity Deformable Mirrors

Abstract

Thermal lensing limits the beam quality of high-power lasers and evokes setpoint-dependent disturbances. Since these effects cannot be corrected outside the resonator, intra-cavity deformable mirrors stand to reason. Based on a Gaussian cavity and a disturbance model with distributed parameters, we derive a discrete-time estimation scheme. Due to the nonlinearities of the optical system, estimating and predicting the disturbance is crucial in order to construct a proper compensation. The presented recursive optimization-based approach considers input constraints in an explicit manner. Finally, the performance of the proposed disturbance rejection is demonstrated by simulations. The algorithm reduces the feedback control effort by more than 90% and improves the tracking behavior of the closed loop.