**6. Conclusions**

We presented experimental results on the optical properties of PIAD titanium dioxide thin films, with a focus on their absorption behavior. In addition to a rather conventional linear optical characterization, TPA coefficients at a wavelength of 800 nm were obtained from laser-induced deflection measurements and were compared to the values reported so far for rutile crystals in terms of a Z-scan technique. It turns out that the TPA coefficients obtained from our LID measurements were very consistent with what has been reported in the literature in terms of manageable models describing the TPA coefficient, such as the Sheik–Bahae model and the ß\_do approach.

We provided a further discussion on the accompanying changes in the refractive index in terms of nonlinear refraction and discussed their possible impact on the elastic light scattering characteristics of dielectric coatings at high light intensities.

**Author Contributions:** Conceptualization, O.S.; formal analysis, O.S., S.W., S.S., and C.M.; funding acquisition, S.W.; methodology, O.S., S.W., and C.M.; project administration, S.W.; software, S.W.; validation, O.S., S.W., S.S., and C.M.; writing—Original draft, O.S.; writing—Review and editing, O.S., S.W., S.S., and C.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Bundesministerium für Bildung und Forschung, grant number 13N10459, and by the European Regional Development Fund, grant number 2016 FE 9045.

**Acknowledgments:** The authors are grateful to Tina Seifert (Fraunhofer IOF) for performing the EDX measurements. We also thank Tsvetanka Babeva for the invitation to submit this study to a special issue of "Coatings" as a feature paper.

**Conflicts of Interest:** The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
