A scratch-resistant and hydrophobic broadband antireflective coating by sol–gel method

A double-layer broadband antireflective (AR) and scratch-resistant coating with hydrophobic surface is fabricated via sol–gel process using acid and base catalyzed silica as precursor solutions. The coating is composed of a dense and a porous silica films of which the refractive indices are high and low respectively, realizing a step-index gradient structure with glass as the substrate. The AR property of the coating is optimized to maximize the amplification yield of the laser disk amplifiers used in high power laser system. The average transmittance of BK7 glass coated in this way increased to more than 99.5% over the range of 500 to 850 nm. After NH3-heat treatment at 200 °C, the scratch-resistance of the coating is improved in a large degree. Trimethylchlorosilane is employed to modify the coating surface to improve the optical stability by resisting moisture. These treatments can ensure that this broadband AR coating is durable for its real application.