## 4 Discussion  
### Impact of the Polishing Suspension Concentration  
As a general point, it should be noted that the measurements presented in Section 3 feature relatively large error bars. Regarding the LIDT measurements, statistically distributed absorbing surface defects may in some cases not be affected by the incident laser irradiation due to the small  
Figure 5: Carbon content of zinc crown glass samples before and after plasma post-processing vs. polishing suspension concentration including trend (dotted line). Figure 6: Laser-induced damage threshold (LIDT) of zinc crown glass samples before and after plasma post-processing vs. polishing suspension concentration including trend (dotted line). spot size of the laser focus. This fact might contribute to the relatively large error bars of the LIDT values which result from the particular values measured at 25 test sites per sample. The observed dependencies as discussed in the present subsection have thus to be treated as a general trend. As presented in Section 3.1, the cerium content at the surfaces of the investigated samples was approximately 0.25 at% after polishing. This value was detected for all polishing suspension concentrations, a correlation between the cerium content within the suspension and surface contamination by this element or polishing agent, respectively, was thus not observed. However, the use of such polishing suspension led to a constant attachment or implantation of cerium at/into the surface as discussed in more detail in Section 4.2. This effect, a saturation of the interaction between the polishing pad or suspension and the glass surface during polishing once a certain concentration of the polishing suspension is reached, was already reported in 2008 by _[PERSON]_ and co-workers [47]. An interesting point is the trend of a decreasing carbon content with increasing polishing suspension concentration. For the origin of the detected carbon, several sources from the manufacturing process should be considered since the glass itself does not contain any carbon according to the manufacturer's datasheet [37]:  
* First, the carbon could originate from the rough grinding process which is usually performed with the aid of cylindrical cup wheels where the bound abrasives are usually made of diamond, i.e., pure carbon. * Second, the application of cooling lubricants during rough grinding is another possible source for carbon since such lubricants are a suspension of water and carbonaceous mineral oil. * Third, the lapping agent used for sample preparation, silicon carbide (SiC), could accumulate within digs and cracks of the glass surface and finally be embedded within hydrated silica which is formed during polishing as introduced in Section 1. In the course of this terminal production step, carbonaceous contaminants could finally arise in the form of wear debris from the used polishing pad made of polyurethane foil. This last aspect could explain the observed behaviour, i.e., an increased carbon content in the case of thin suspensions. Here, wear preferentially occurs between the polishing pad and the glass surface due to direct contact. The higher the concentration of the suspension, the more polishing agent grains are found in between the pad and the surface, consequently reducing direct wear. The presence of carbon turns out to be the main reason for a decrease in LIDT. Since the cerium content is quite constant for all polishing suspension concentrations as mentioned in Section 3.1, the impact of this parameter on the LIDT can be assumed to be constant as well. In contrast, the LIDT and the carbon content tends to depend on the polishing suspension concentration, see Figure 4. The increase in LIDT with decreasing carbon content can be explained by the fact that a reduction in surface-adherent carbon and carbonaceous compounds corresponds to a reduction in absorbing contaminants which may act as precursor for laser damage.