Theoretical and experimental investigation of precise and dynamic beam shaping for laser materials processing

• Applicant: Dr.-Ing. Annika Bonhoff
• Subject Area: Joining and Separation Technology ; Production Automation and Assembly Technology
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 387868000

In many procedures of laser materials processing, the power density distribution (PDD) of the laser beam strongly impacts the resulting temporal and spatial temperature profile and thus the processing result. Thus, for an efficient, high-quality processing, an appropriate adaptation of the PDD – especially for high laser power – is required. Currently, beam shaping approaches, that principally enable the requested dynamic flexibility, are only applicable for low laser power. Thus, in the previous project, a beam shaping approach has been developed that first performs the beam shaping with a so-called LCoS (for liquid crystal on silicon) and afterwards amplifies the resulting laser beam in power. This approach has been shown to be promising, but a number of further research questions arose that shall be answered in the described project.At first, in the previous project, crosstalk has been identified as an error source in the beam shaping procedure. This crosstalk occurs between different pixels of the segmented LCoS wherein the addressing of a single pixel also significantly impacts the neighbored pixels. As currently no strategy has been described that compensates this for laser beam shaping, one goal of this project is to develop a corresponding simulation and compensation methodology. It is furthermore planned for the project to analyze how a derivation of the required phase mask, which is impressed on the laser beam by the LCoS, can be performed by machine learning. In the previous project, a computation algorithm has in fact been developed for the computation of this phase mask. However, the computation time of this algorithm for a single phase mask is high so that a real time computation, which is required for a dynamic beam shaping in many applications, cannot be obtained.Finally, in the previous project, beam shaping has been investigated without considering its impact on the temperature profile. As this actually is the relevant quantity for a successful processing result, a coupling of the beam shaping method to a simulation tool for the solution of an inverse heat conduction problem is planned for the suggested project. This simulation tool, which has already been developed, enables the computation of a PDD that is required to generate a prescribed temperature profile. By realizing such a coupling, it shall be investigated how an adaptation of the phase mask regarding an optimization of the resulting temperature profile (instead of the PDD) leads to an additional increase in performance of the combination of LCoS and amplifier. By dealing with these three research questions, a successful realization of an application adapted, precise and dynamic beam shaping is enabled also for high power laser beams.

• DFG Programme: Research Grants