## 3 Results and Discussion
### Chemical Composition of the Surface and Water Bath
Their results showed that ablation products are rich in carboxylic groups and carbon, but did not correspond directly to hydrolysis products of polymer. It is also evident, that variation of voltage has no direct impact on chemical composition, which corresponds well with the fact that absorbed energy is invariant towards this parameter. Remarkable difference in concentrations of C and O in dependence of detection angle can only be observed at treatment fluence of 8 mJ\(\cdot\)cm\({}^{-2}\), similarly as in case of pristine PET. This phenomenon most likely originates from considerably low absorbed energy when the ablation and photothermal cleavage of macromolecules is low. To reveal the mechanism of surface structure development on laser treated polymer, identification of the rate of material ablation was accomplished. To address this issue, ICP-MS analysis of the water bath used in underwater laser treatment, aiming to total carbon content (TCC), was accomplished. Those results are summarized in Figure 7a,b. Changes in the TCC correspond to the release of low molecular weight polymer ablation product to water environment due to laser modification. Figure 7a shows dependence of TCC on applied voltage at fixed laser fluence of 8 mJ\(\cdot\)cm\({}^{-2}\). Compared to measured TCC background in fresh water (blue line, 1.2 \(\pm\) 0.3 mg\(\cdot\)L\({}^{-1}\)), TCC in the bath increased approximately one order of magnitude after laser processing. It is clearly visible that applied voltage has no influence on TCC, which is in good concordance with results obtained from AR-XPS analysis, suggesting limited material removal from the PET surface at low fluencies. Additionally to that, Figure 7b summarizes the values of TCC measured for different laser fluence applied at fixed voltage of 25 kV. From the presented data, one can see exponential dependence of the amount of ablated material on applied fluence. As the absorbed energy grows, increase of TCC is detected, pointing to massive polymer ablation. Data presented in Figures 5 and 6 unambiguously demonstrate the enrichment of the water bath by the low-molecular polymer degradation products,  
Figure 7: Total carbon content (TCC) determined by ICP-MS in water bath after laser processing of PET: (**a**) TCC in dependence of applied voltage at fixed value of laser fluence of 8 mJ\(\cdot\)cm\({}^{-2}\) and (**b**) TCC independence of applied laser fluence at fixed value of applied voltage of 25 kV. Blue line (solid one) in (a) represents background TCC content in pure water together with measurement error (dash one). which prove that ablation mechanism is the governing process of surface nanostructure formation. Besides others, this finding contributed to reveal one of the challenges of present material research, namely the mechanism of LIPPS formation. Great efforts have been made to address this issue so far, considering various approaches involving UV-Vis spectrometry [17] or gravimetry [18], which outputs were often loaded with considerable statistic error. Right the use of water bath and thus capturing of low molecular weight product of ablation process into the media allowed to determine TCC by ICP-MS method.