Physical Investigation of Self-Induced Laser Focus Displacement during Photodisruption with Ultrashort Laser Pulses

• Applicant: Dr. Tammo Ripken
• Subject Area: Biomaterials ; Synthesis and Properties of Functional Materials ; Medical Physics, Biomedical Technology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269706059

A so far unknown and uninvestigated axial laser focus displacement was detected during fs-laser application of optically transparent materials. The laser disruption zone moves towards the laser out of the geometrically expected focus region. Hence, the theoretically possible precision of laser cuts in the range of the focal spot cannot be achieved. Unintended axial displacements of up to several tenth of micrometer were measured. In common laser applications, this effect is suppressed by choosing appropriate laser repetition and scanning parameters. To our best knowledge, there exists no explanation of this phenomenon caused by ultrashort laser pulses within the literature. In the following request for funding, the reason of the phenomenon shall be explained and hence methods to avoid this effect will be determined. Therefore, parameters as optical density of the regarded materials and optical breakdown threshold in dependence of previous pulses will be analyzed during the cutting procedure. Furthermore, computer simulations will be performed to confirm the experimental results. Based on a variety of materials, the effect will be categorized and referred to basic physical material properties. Prospectively, a suppression of this unsatisfied cutting quality can be performed on purpose.

• DFG Programme: Research Grants
• Cooperation Partners: Professor Dr. Holger Lubatschowski; Professor Dr. Matthias Ochs