Enhanced antireflective and laser damage resistance of refractive-index gradient SiO₂ nanostructured films at 1064 nm

A facile sol-gel procedure was employed to create refractive-index gradient SiO₂ antireflective (AR) films. A monolayer film, characterized by the porous crosslinking framework, was fabricated with a designed volume ratio mixture both with colloidal silica suspension and soluble organic polysiloxane. The upper layer for the bilayer film was a hexamethylisilazane (HMDS) modified colloidal silica suspension, leading to the film surface transfer to hydrophobic. The strategic design of nanostructures in the bottom and upper layers resulted in a refractive-index gradient SiO₂ film with enhanced AR properties. The bilayer film demonstrated a transmittance of 99.5% at 1064 nm, accompanied by a notable reduction in reflectivity. Moreover, the laser-induced damage threshold of the bilayer film was increased by 30%, rising to as high as 24.7 J/cm². The SiO₂ nanostructured film both showed a refractive-index gradient structure with excellent AR properties and exhibited good laser damage resistance.