# A Review on Ultrafast Laser Enabled Excellent Superhydrophobic Anti-Icing Performances
## 2 Ultrafast Laser-Fabricating Micro-Nanostructured Superhydrophobic Surfaces
### Ultrafast Laser Micro-Nano Fabricating
This phenomenon is mainly attributed to the pulse durations of ultrafast laser (picosecond and femtosecond laser) being shorter than the electron-lattice relaxation time (\(\sim\)\(10^{-12}\) s). Hence, less heat is transferred, causing a smaller thermal effect. For the pulse input number, the micro-nanostructure sizes and morphologies are directly influenced. Figure 5c exhibits the evolution of micro-nanostructures with the pulse input number. It is found that the particles can be flexibly controlled not only in the wide range of nanoscale, sub-microscale, fine-microscale, microscale, and coarse-microscale but also with various structural sizes, including heights and intervals [100]. Figure 5: Mechanisms and morphologies of ultrafast laser micro-nano fabrication. (**a**) Timescales and intensity of main phenomena during and after irradiating a solid with a femtosecond laser. (**b**) Evolution of surface morphologies and processing quality with the laser wavelength (reproduced with permission from [101] (copyright (2021) Elsevier) and [102] (copyright (2019) Elsevier). (**c**) Evolution of micro-nanostructure sizes with the laser pulse input number (reproduced with permission from [100]. Copyright (2015) Elsevier). Besides the fundamental laser parameters, processing environments also play a significant role in structural morphologies and chemical elements. For example, we once adopted a femtosecond laser to process Ag samples in air and Argon atmosphere [103]. It was found that more nanoparticle clusters and less oxide were generated in Argon. In the meantime, by ablating NiFe in the NH\({}_{3}\) atmosphere, we also fabricated more abundant nanoclusters than in the air [104]. These discoveries confirm that the processing atmosphere has a great influence on micro-nanostructure morphologies. Based on diverse processing parameters and environments, ultrafast laser-fabricated micro-nanostructures could be easily tuned to further realize the fine control for superhydrophobic states. [PERSON] et al. achieved the superhydrophobic state tunability from the Wenzel state to the CB state by simply changing the laser scanning speeds on the copper material [51]. The superhydrophobic state evolution was ascribed to the changes in microstructure sizes and nanostructure amounts, where lower scanning speeds could induce deeper microstructures and more abundant nanostructures to contribute to the CB state. [PERSON] et al. discovered the controllable wettability on Polyimide film via femtosecond laser thermal accumulation engineering [105]. By regulating local thermal accumulation effects, different micro-nanostructures were induced, realizing the wettability changes from superhydrophobicity (\(\sim\)3.6\({}^{\circ}\)) to superhydrophobicity (\(\sim\)151.6\({}^{\circ}\)). [PERSON] et al. adopted a femtosecond laser to fabricate a temperature-response ceramic surface with switchable wettability [106]. Superhydrophobic and superhydrophilic interfaces were reversibly and repeatedly transited after alternate heating treatments. It was confirmed that laser-induced micro-nanostructures contributed to the removal and re-absorption of organic compounds, thus resulting in the wettability transition.