# A Review on Ultrafast Laser Enabled Excellent Superhydrophobic Anti-Icing Performances
## 4 Advances and Challenges of ULSASs
### Passive/Active Combined Superhydrophobic Anti-Icing Surfaces
#### 4.2.2 Photothermal/Superhydrophobic Anti-Icing Surfaces  
In contrast to electrothermal deicing methods, the photothermal/superhydrophobic anti-icing technology mainly utilizes solar energy in nature to convert into heat, eventually realizing passive/active combined deicing [171]. It is an environmentally friendly deicing technique without consuming any fossil fuel. Based on the photothermal conversion principles, photothermal SHSs can also be divided into two types: (i) the SHSs with structural light traps [82; 172]; and (ii) the SHSs with the new phases that own the high solar-to-heat conversion efficiency [163; 173; 174]. Adopting various micro-nanostructures and the generated new matters enabled by ultrafast lasers, the two types of methods have been widely explored. [PERSON] et al. were inspired by moth eyes to fabricate the biomimetic micro-nanostructures with a femtosecond laser [175], as shown in Figure 17a. The surfaces were composed of micro-mountain arrays with micro-nanoparticles, which constructed a well-structured light trap. Under one-sun illumination, the surface temperature can rise rapidly and exceed 80 \({}^{\circ}\)C in 300 s. Even a large ice cube could melt and shed off the surfaces within 240 s under sunlight. [PERSON] et al. considered that the adhered condensates in extremely high-humidity conditions could hinder the photothermal properties and induce condensation freezing. Hence, they fabricated hierarchically structured materials by ultrafast pulsed laser deposition (PLD) technology (Figure 17b) [176]. The generated iron oxide during laser irradiation was deposited densely on substrates, not only constructing the strong light traps but also further contributing to the photothermal conversion by the thermoplasmonic effect of iron oxide nanoparticles. In the extreme environment with a temperature of \(-\)50 \({}^{\circ}\)C and a supersaturation degree of \(\sim\)260, the photothermal anti-icing properties of the surfaces could be well maintained and the equilibrium temperature could exceed 0 \({}^{\circ}\)C under one-sun illumination owing to their superior condensate self-removing and high photothermal conversion capability.  
Figure 17: Photothermal/superhydrophobic anti-icing surfaces. (**a**) Highly effective photothermal/superhydrophobic anti-icing properties enabled by the biomimetic laser-fabricated structures(reproduced with permission from [175]. Copyright (2021) Elsevier B.V.). (**b**) Solar anti-icing surfaces with enhanced condensate self-jumping in extremely low-temperature and high-humidity environments (reproduced with permission from [176]. Copyright (2021) PNAS).  
Compared to the single passive superhydrophobic anti-icing method, the passive/active combined anti-icing methods could better withstand complicated and volatile environments. However, how to realize low-cost large-scale fabrication is still a key problem for practical applications [11; 13]. Meanwhile, different application scenarios also propose more requirements, such as the specific surface roughness and the bonding between surfaces and heating elements in the aviation field.