MgF2-based conformal antireflection coatings on highly curved lenses by atomic layer deposition

Antireflection (AR) coatings are crucial for a myriad of optical applications. The demand for conformal AR coatings over nonplanar substrates, such as a 3D glass or curved lenses, is increasing. In this study, atomic layer deposition (ALD) was utilized to deposit multilayer AR films composed of MgF2, SiO2, Al2O3, and HfO2. Notably, MgF2 thin films are desirable as the top layer due to their low refractive index (sub-1.4), wide spectral transparency from the ultraviolet to the infrared region, and considerable chemical stability. First, the thickness uniformity of the four distinct films was optimized using the thermal ALD method, and then their individual optical properties were investigated. This information supported the design of a seven-layer AR film, and subsequently, the AR layers were deposited onto substrates with highly curved lenses. Then, the optical performance of the coated lenses, with a focus on reflectance, was measured. Our measurements indicate that conformal AR coatings on lenses with pronounced curvature were successfully deposited. The research highlights the potential for achieving highly uniform AR coatings with precise optical control in areas such as medical optics, photonic integrated circuits, and metasurface devices. In conclusion, this study conclusively demonstrates the superiority of ALD-based AR coatings on complex geometric surfaces, offering an effective alternative to the traditional physical vapor deposition methods when confronted with their intrinsic constraints.