Visualization of nanometer scale defects responsible for optical loss and laser induced breakdown in binary coating materials for the UV spectral region

• Applicant: Professor Dr. Detlev Ristau
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317442515

Nowadays UV optics are considered as important key components for many innovative applications in photonics andlaser technology. Among many others, the large areas of UV laser material processing, laser medicine or particularly,semiconductor lithography impose demanding challenges onto the quality of optical UV-components. Both the opticalloss and the laser power handling capability of the components are of outmost importance for the success of a laserconcept and its applications. Laser induced breakdown of optical components occurs at much lower irradiationintensity as predicted by theories based on damage due to photoionization. Since decades, it is a well-acceptedinterpretation that the reduction of optical damage threshold, and also the increase of optical losses are caused bydefects, such as nanometer-sized particles, voids, and the interfaces as well as stoichiometric deficiencies. Thesedefects could be embedded in the thin coating layer, at layer- or substrate interfaces, or below the substrate surface.Despite the broad acceptance of this theory in the optical community, mostly these suggested defects either remainedinvisible for direct observation, or it was not possible to verify their influence on the damage behavior directly.In the proposed research endeavor, it is planned to identify and study the dominant contributions to optical losses andlaser induced breakdown in optical coatings for UV-laser applications. As mentioned before, the reason for thischallenge is the suggested defect size of a few nanometers. The approach within this proposal for identifying nanodefectsresponsible for optical breakdown, is double-tracked: On the one hand, corresponding artificial defects shall beincorporated in state of the art optical coatings to reproduce optical damage behavior, and on the other hand an opticalprobe techniques shall be developed, to obtain topographies of optical properties on the nanometer scale.

• DFG Programme: Research Grants