Fraunhofer Institute for Microstructure of Materials and Systems IMWS
SEM images of the surface and the FIB-prepared cross-sections of typical defect patterns on laser mirrors.
Analysis of laser mirror coatings
The “Optical Materials and Technologies” business unit at Fraunhofer IMWS offers customized solutions for the characterization and failure analysis of optical coating systems. For example, state-of-the-art methods are available for the examination of (damaged) laser mirrors.
A laser mirror damaged in a lifetime test (LIDT) was examined using a variety of methods.
Failure mechanism in an IBS laser mirror: the process-related noble gas (Ar) agglomerates due to the energy input of the laser irradiation, which leads to bubble formation in the layer system and ultimately to delamination, destroying the mirror.
Our high-resolution thin-film analysis methods enable precise analysis of the microstructure and chemical composition of materials. The techniques available include:
- FIB-SEM (Focused Ion Beam & Scanning Electron Microscopy): This method allows detailed imaging of surfaces and cross-sections to determine the structure of coating systems at the nanometer level and is used to locate defects.
- HR-(S)TEM (High-Resolution Scanning Transmission Electron Microscopy): This allows us to analyze the microstructure and chemical composition of materials at the atomic level.
- ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry): This technique enables surface analysis and high-resolution depth profiling to identify impurities down to the ppb range, for example.
These methods enable comprehensive characterization of coating systems and their properties. One example of our expertise is the analysis of laser mirror coatings. To improve the performance of the mirrors, we performed thin film and failure analysis on damaged mirrors after a lifetime test (LIDT). The analysis included:
- Evaluation of damage caused by laser induced damage threshold tests (ns-LIDT and fs-LIDT): Evaluation of the cause of coating failure
- Thin-film analysis: Identification of the original coating structure and composition to verify the deposition process for layer thickness accuracy and impurities
The results of these analyses show how our methods contribute to the identification of impurities and the evaluation of surface and interfacial roughness. They also reveal the origin of particles/contaminations, the crystallinity of individual layers, the layer porosity, and the distribution of chemical elements. This makes an important contribution to ensuring the performance and longevity of laser mirrors in industrial applications, such as in optical devices like microscopes, optical communication systems for signal transmission, or for use in lithography processes in the semiconductor industry.
(December 18, 2025)