# A Review on Ultrafast Laser Enabled Excellent Superhydrophobic Anti-Icing Performances
## 1 Introduction  
Icing phenomena have brought tremendous troubles in many fields such as telecommunication, transportation, energy, etc. [1, 2, 3, 4]. Especially in aviation applications, the formed and accumulated ice on airplanes greatly damages aerodynamic properties [5, 6, 7]. It has been shown that mm-thick ice on airfoils will result in about 30% loss of lift force per unit area, eventually causing catastrophic accidents [8, 9]. In recent years, many crashes related to icing have taken place. To eliminate ice formation and build-up, some conventional anti/deicing technologies such as electrothermal, pneumatic, and ultrasonic deicing have been developed and widely used [10, 11, 12]. This notwithstanding, such active deicing strategies tend to be extremely wasteful energy, are of low-efficiency, and not environmentally friendly [13]. These drawbacks overwhelmingly restrict their applications in situations such as for diminutive airplanes from drones to warcraft and some industrial applications from pipelines to power lines [14, 15]. Therefore, novel anti/deicing technologies are in urgent need of researching and developing to meet the application demands. Inspired by the water repellency of the lotus in nature, superhydrophobic surfaces (SHSs) have been one of the most promising candidates for achieving passive anti/deicing [16, 17]. With extremely high contact angles of \(>\)150\({}^{\circ}\) and low sliding angles of \(<\)10\({}^{\circ}\), SHSs can significantly reduce the solid-liquid contact area to repel external water droplets in timeand thus keep surfaces dry [18; 19; 20]. The unique properties have attracted a flurry of researchers and engineers to pay great attention to moving SHSs toward anti-icing applications [21; 22; 23; 24]. Figure 1 shows the increasing number of published articles on the topic of \"anti-icing\" and \"superhydrophobic anti-icing\" in recent years. Among these, papers about superhydrophobic anti-icing account for about one-quarter of all publications, showing their dominant role. However, with the deepening of research, it is found that superhydrophobic surfaces cannot always eliminate icing issues and have greater ice adhesion strengths than smooth pristine surfaces in some cases [25; 26]. With regard to mechanisms, superhydrophobicity is mainly attributed to a large number of trapped air pockets among micro-nanostructures, where a triple-phase solid-liquid-gas interface will be constructed. However, the air pockets are very fragile. Once they are broken, greater ice adhesion will be generated owing to the mechanical locking between ice and micro-nanostructures. In this case, the micro-nanostructures also provide more ice nucleation sites to promote theicing process [27; 28; 29]. These negative results have given rise to a number of debates on whether SHSs are advantageous for anti-icing applications. [PERSON] et al. compared different types of anti-icing surfaces, including superhydrophobic surfaces, slippery surfaces, and hydrated surfaces. They emphasized the decisive role of surface structures on anti-icing properties [30]. To further understand the relationship between superhydrophobicity and icephobicity and explore the optimized superhydrophobic anti-icing surfaces, fabricating and easily controlling micro-nanostructures is of great significance. To date, many state-of-the-art strategies have been developed to fabricate micro-nanostructures, including chemical etching, machining, 3D printing, sol-gel methods, laser processing, and others [31; 32; 33; 34; 35]. Among these, ultrafast laser micro-nano fabricating, as a novel top-down processing strategy, shows the superior advantages of nm-accuracy, contact-free, and highly programmable processing without material dependence. This method is not only easy for fabricating surface micro-nanostructures but also greatly promising for practical applications [36; 37; 38; 39] (Table 1).