## 5 Conclusions  
The results presented in this work clearly show that the laser-induced damage threshold of the investigated glass is directly related to surface contamination by carbon. The highest LIDT was found for the lowest contamination which occurred in the case of the highest polishing suspension concentration. In contrast, surface contamination by the actual polishing agent, cerium, does not depend on the polishing suspension concentration. The results thus suggest that classical polishing of laser optics surfaces with high polishing suspension concentration allows increasing the LIDT. However, this assumption has to be verified in the frame of further ongoing investigations due to the extraordinarily high number of possible configurations during manufacturing in terms of the glass type, the used abrasives (especially carbon-based ones such as silicon carbide or diamond), the pH-value of the polishing suspension, the used tools and polishing pads, etc. The increase in carbon contamination with decreasing polishing suspension concentration is most likely due to a higher wear between the polishing pad made of carbonaceous polyurethaneand the glass surface, due to a reduced number of polishing grains within the suspension. Thus, the effective direct contact area of the pad and the glass is bigger, consequently leading to increased formation of carbonaceous wear debris from the polishing pad according to the Preston equation [6]. Such debris can adhere on the surface and also accumulate in the formed silica layer or even penetrate into the glass bulk material by diffusion. In this context, the pH-value of the polishing suspension gains importance [58]. This value moreover influences the magnitude of near-surface forces during polishing [59] and the accompanying wear and formation of wear debris. As mentioned above, this point is thus to be investigated in future work. Apart from an increased carbon contamination, another possible mechanism for the decrease in LIDT with decreasing polishing suspension concentration could be material densification due to local load induced by the polishing tool. Such densification leads to an increase in index of refraction [60] and absorption, respectively. Actually, such an increase in index of refraction with decreasing polishing suspension concentration was qualitatively observed and verified by ellipsometric measurements. The significant increase in LIDT after plasma post-processing is obviously directly related to the removal of carbon from the glass surfaces. The effect of plasma-induced cleaning of glass by the removal of carbonic contaminations surfaces is well-known and used in quite different fields of application [30]. However, the use of plasmas for increasing the LIDT of optics is a comparatively new area of research (compare Section 1). Plasma post-processing as presented in this work stands out due to the operation at atmospheric pressure and comparatively low temperature, the use of the standard process gas argon and the short treatment duration of 60 s. This approach can be integrated into existing optics production chains quite easily and thus features high potential for industrial processes for surface finishing of high-power laser optics. [PERSON] conceived and designed the experiments, analysed the data and wrote the paper; [PERSON] prepared the samples, performed the experiments and analysed the data. This research received no external funding. The authors thank the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) and the Ministry for Science and Culture of Lower Saxony (Ministerium fur Wissenschaft und Kultur, MWK) for funding the laser source which was used for LIDT measurements. Further, the authors thank [PERSON], [PERSON], and [PERSON] from the University of Applied Sciences and Arts in Gottingen for their help during the preparation and analysis of the investigated samples.