Within high power laser applications average power is increasing continuously. Volume absorption in specialized glass material is comparably low, so the focus for quality optics is on the surfaces and the coating. Given the surface quality is sufficient, subsurface defects neglectable, the coating absorption will finally drive local heating.

A successful one-time qualification of a coating recipe will unfortunately not give enough evidence to guarantee the absorption level for coating batches in production. As well an optimization of coating parameters to achieve low absorption levels is not possible without repetitive measurements. Therefor an appropriate device is needed in house to measure batches inline if ppm level absorptions needed to be guaranteed.

Fraunhofer IOF developed and built the device, based on the principle of laser induced deflection (LID), SILL optics ordered for their serial manufacturing and does the statistical metrology system analysis to ensure an accurate and stable process in manufacturing.

The paper and the talk will tell in detail about the principle, the setup, calibration and the statistical measurement for different combinations of substrates, coatings and laser wavelengths. It will finally show, how this measurement will be implemented in the quality control of our high-power laser optics, beam expanders, f-Theta and focusing optics.