在SiO2溶胶合成阶段进行化学改性，将六甲基二硅氮烷（HMDS）引入SiO2溶胶，制得稳定的胶体,胶体中SiO2纳米颗粒表面的亲水性Si-OH基团被疏水性的Si-O-Si(CH3)3基团取代。采用旋转法在磷酸二氢钾(KDP)晶体表面涂膜，涂膜晶体峰值透射率99%以上。膜层光学均匀性良好，表面粗糙度均方根值为0.94 nm。膜层疏水性能好，水接触角达到140°。涂制疏水性SiO2基减反膜的KDP晶体无需热处理就具有较好的疏水防潮性能，与目前激光器使用的防潮减反双层膜相比，在室温高湿度条件下涂膜晶体透射率下降情况大致相当。旋转涂膜可以有效解决三倍频晶体入光面与出光面共3个波段需减反的问题。

The Si-OH group on particle in the silica colloidal suspension is modified to Si-O-Si(CH3)3 non-polar hydrophobic group using hexa-methyl-disilazane (HMDS). The organic modified silica antireflective (AR) coatings that coated on potassium di-hydrogen phosphate (KDP) crystal and silica glass substrates by spinning method, has good moisture-resistant property. The transmission of coated substrate is above 99%. The optical roughness root-mean-square value is 0.94 nm and the water contact angle of coating is about 140°. The HMDS modifies SiO2 sol in non-polar solvents which need no treatment can be used in KDP crystals. In the condition of the room temperature and high humidity, the transmittance decrease of KDP crystals with the moisture-resistant(MR) AR coating is equal to the MR/AR two-layer coating. The reflection losses at three wavelengths from two surface of the tripling crystal can be minimized by spin coating.