In the process of realizing double-wavelength broadband antireflection (AR) coatings, it is very important to control the refractive index in a wide range, but at present, many methods of adjusting the refractive index are too complex or expensive. Here, a simple and inexpensive sol–gel route is proposed to prepare the superhydrophilic silica (SiO₂) thin films having ultra-low refractive indices by the SiO₂ particles surface corrosion with hydrofluoric acid (HF) in sol; this treatment effectively reduces the refractive index of the coating from 1.22 to 1.11. The formation mechanism of the coatings with ultra-low refractive index was discussed in detail. The corrosion of HF on the particles surface significantly improves the hydrophilicity of the coating, and reduces the water contact angle of the coating from 27° to 2°. The bottom layer is prepared by mixing the acid–base complex silica sol. When the refractive indices of the bottom and top layers were set as 1.29 and 1.13, the double-layer double-wavelength AR coating with excellent optical properties has the transmittance of 99.95% and 100.00% at 532 and 1064 nm, respectively.

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在实现双波长宽带减反射（AR）涂层的过程中，将折射率控制在一个很大的范围内是非常重要的，但是目前，许多调整折射率的方法过于复杂或昂贵。在此，简单且廉价的溶胶-凝胶途径提出以制备超亲水是二氧化硅（SiO ₂）通过将SiO具有超低折射率薄膜₂溶胶中的氢氟酸（HF）对颗粒表面的腐蚀；这种处理有效地将涂层的折射率从1.22降低到1.11。详细讨论了超低折射率涂层的形成机理。HF在颗粒表面的腐蚀可显着改善涂层的亲水性，并将涂层的水接触角从27°降至2°。底层是通过混合酸碱复合硅溶胶制备的。当底层和顶层的折射率设置为1.29和1.13时，具有优异光学性能的双层双波长AR涂层在532和1064nm处的透射率分别为99.95％和100.00％。

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