High wear resistant double-layer antireflection coatings for near-infrared vehicular lidar

The lidar operates at 905 nm is considered to have essential application values in automotive autonomous driving. The antireflection coatings made by magnetron sputtering commonly used in industry have the problem of insufficient wear resistance, which is difficult to adapt to the harsh outdoor environment. The sol-gel method combined with high-temperature curing process was used to provide a solution of high wear resistance and low cost for antireflection coatings applied to vehicular lidar which operated at 905 nm, and the influences of curing temperature, concentration of hydrochloric acid (HCl), water content in weak acid environment on refractive index of TiO₂ were studied. The optical and mechanical properties of the coatings with different underlying curing methods were evaluated from the reflectivity, roughness, hardness and wear resistance. The results show that the coatings have excellent anti-reflection performance at the wavelength of 905 nm, the reflectivity is less than 1% when the incident angle is 15° and less than 5% when the incident angle is 60°, and the minimum roughness is 0.005 μm, which generally meets the optical requirements of the lidar with a horizontal angle of 120°. The coatings show the excellent capability of enduring harsh environments, with pencil hardness of 8H and withstanding 8 000 times of reciprocating friction without perceptible damages.