Spatial light assisted femtosecond laser direct writing of a bionic superhydrophobic Fresnel microlens arrays

High quality imaging and self-cleaning function are two significant factors for Fresnel Microlens Arrays (FMLAs) to operate properly in outdoor environment. Bionic superhydrophobic FMLAs are explored for outdoor uses due to their ability allowing free rolling down of water droplets taking away dust particles. Current photolithographic method of fabricating FMLAs involves multi-processing steps, which increase the complexity of the microlens array structure as well as reduces the optical imaging capability of the lenses. In this study, we report a method for creating bionic superhydrophobic FMLAs by integrating the Nepenthes Alata crescent structures with FMLAs fabricated by spatial light assisted femtosecond laser direct writing, i.e. Two-Photon Polymerization (TPP). The fabricated FMLAs were further modified with Perfluorooctyltrimethoxysilane (F13) to enhance hydrophobicity and surface uniformity. Results show that the optimized bionic FMLAs exhibit superhydrophobicity in different liquid media and excellent self-cleaning ability. The water contact angle (CA) reached 156.3°, a low rolling angle of 4.7°, and surface adhesion force of 25.5 μN. The FMLAs designed have excellent imaging characteristics and focusing ability. This research provides insights into the fabrication and performance optimization of bionic superhydrophobic FMLAs, offering potential applications for outdoor optical systems.