Control systems for adaptive optical systems in high power laser resonators

• Applicants: Professor Dr. Thomas Graf; Professor Dr.-Ing. Oliver Sawodny
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: from 2014 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257920601

• Final Report Year: 2023

Final Report Abstract

High-power lasers are used in a wide range of applications and in numerous material processing methods. As there are high quality requirements in industry, good beam quality is required over a wide range of the output power. The vision of a flexible and universal tool is countered by principle-related power-dependent sources of perturbation. In many cases, less than half of the supplied power is converted into usable laser radiation, meaning that the perturbation power can be expected to be of the same order of magnitude as the usable laser power, which further reduces the beam quality and efficiency at high output powers and cannot or only insufficiently be corrected outside the laser device. The use of adaptive optical actuators within the laser promises great potential to compensate for these disturbances. Nevertheless, their application in high-power lasers is still in its infancy due to the strong physical coupling of all components. Consequently, the topic raises numerous research questions at the interface between laser and system technology. As part of the present research project, pneumatically and optically addressed deformable mirrors were developed and their pneumatic and thermo-mechanical behavior as well as the influence of their variable refractive power on the optical system were modeled and analyzed in detail. Based on an elaborate model order reduction, the actuator technologies were integrated into a model-based control loop and a control system. In combination with the estimation of thermally induced perturbation, a significant increase in beam quality over a large power range was demonstrated both simulatively and experimentally. Furthermore, the control of several beam parameters in the resonator was demonstrated experimentally with the help of several pneumatic actuators, which lays the foundation for a power-scalable pulsed laser operation. In addition, concepts for a control of the pulse duration were developed and non-linear effects between higher-order transverse laser modes were investigated.

Publications

• Designing pneumatically actuated deformable mirrors: control of circular plates with varying thickness. 2019 American Control Conference (ACC) (2019, 7), 614-619. IEEE.
  Schmidt, Kevin; Raisch, Adrian & Sawodny, Oliver
  
• Energy-optimal disturbance feedforward control for constrained deformable mirrors with thermoelastic actuation. 2019 IEEE International Conference on Systems, Man and Cybernetics (SMC) (2019, 10), 107-112. IEEE.
  Schmidt, Kevin; Graf, Thomas; Ahmed, Marwan Abdou & Sawodny, Oliver
  
• Entwurf deformierbarer Spiegel für den Einsatz in Hochleistungslasern. tm - Technisches Messen, 86(3), 121-130.
  Schmidt, Kevin; Piehler, Stefan; Dannecker, Benjamin; Dietrich, Tom; Raisch, Adrian; Graf, Thomas; Abdou Ahmed, Marwan & Sawodny, Oliver
  
• Inversion of coupled parabolic PDEs with distributed acting inputs for feedforward controlling thermoelastic deformations. 2019 American Control Conference (ACC) (2019, 7), 3883-3888. IEEE.
  Schmidt, Kevin & Sawodny, Oliver
  
• On compensating thermal lensing in high-power lasers using intra-cavity deformable mirrors. IFAC-PapersOnLine, 52(15), 1-6.
  Schmidt, Kevin; Dietrich, Tom; Dannecker, Benjamin; Graf, Thomas; Ahmed, Marwan Abdou & Sawodny, Oliver
  
• “Störgrößenkompensation und Strahlformung durch deformierbare Spiegel in Hochleistungslasern”, 53. Regelungstechnisches Kolloquium, Boppard, Germany, 2019
  Sawodny, K. & Schmidt, O.
  
• Towards adaptive high-power lasers: Model-based control and disturbance compensation using moving horizon estimators. Mechatronics, 71(2020, 11), 102441.
  Schmidt, Kevin; Beirow, Frieder; Böhm, Michael; Graf, Thomas; Abdou Ahmed, Marwan & Sawodny, Oliver
  
• “Störgrößenkompensation und Strahlformung für adaptive Hochleistungslaser durch deformierbare Spiegel“; Dissertation, Shaker Verlag, 2020, ISBN: 978-3-8440-7664-6
  Schmidt, K.
  
• Closed-loop controlled compensation of thermal lensing in high-power thin-disk lasers using spherically deformable mirrors. Laser Physics Letters, 18(2), 025002.
  Beirow, Frieder; Schmidt, Kevin; Sawodny, Oliver; Graf, Thomas & Ahmed, Marwan Abdou