Correlation between chemical structural changes and laser fluence in femtosecond laser processing of polydimethylsiloxane

The dependence of the ablation rate on the laser fluence was measured in femtosecond laser processing of polydimethylsiloxane, and the slope of the ablation rate tended to change to three ablation regimes. The laser-irradiated area was analyzed using Raman and photoluminescence spectroscopy to investigate the cause of the changes in the slope in terms of chemical structural changes. We will show that microscopic observation of the cross-sectional sample enables the analysis of grooves with a high aspect ratio that could not be measured by conventional observation from the sample surface. This allows us to discuss the correlation between the ablation rate and chemical structural changes over a wide range of fluences up to the high fluence regime. As a result, it was found that in the low fluence regime, the photochemical process is dominant with the gentle slope of ablation rate, while both photochemical and photothermal processes lead to an increase in the slope in the middle fluence regime. Moreover, the steep slope in the high fluence regime was induced by high temperatures where carbon–carbon bond formation takes place.