Lehrstuhl für Fertigungstechnologie, Universität Erlangen-Nürnberg

Closed-Loop-Control of Laser Power and Focus Parameters of CO2 High Power Lasers

Datum: 20.12.1996



  • Prof. Dr.-Ing. Dr. h.c. M . Geiger
  • Prof. Dr. rer. nat. J. Christiansen, Erlangen

The aim of the thesis was the development of a control circuit for high power CO2 laser beams. This combines innovative sensors and actuators to form a complete closed-loop-control. For online diagnostics of the laser beam parameters, measurement systems based on thermoelectrical detectors with extremely high dynamics (atomic layer thermopiles) were developed. Integration into a commercial laser system with flying optics and rf-excited laser source allows comprehensive analysis of disturbances. The resulting control system was devided into two subsystems for separate optimization. Laser beam power is controlled through a two step controller using the rf-generator as actuator. This improves power stability more than the factor 100 without negatively affecting laser efficiency. The focus parameters are determined online through indirect measurements in the vicinity of the focussing optics. The highly dynamic adjustment occours through two adaptive optics. This system fulfills the fundamental requirements for integration into commercial laser systems due to its compact design, ease of application and avoidence of moveable mechanical components.