Preparation And Properties Of Sol-gel Multi-functional SiO₂ Antireflection Coating

As the most important inertial confinement fusion(ICF)driver,high-power solid-state devices have been a research hotspot,and their laser transmission efficiency is an extremely important indicator for the device.The results show that the laser reflection caused by the abrupt change of the refractive index at the interface of the vacuum/optical components is one of the important factors that affect the laser transmission efficiency of the high power solid-state laser device.Therefore,optical components coated with high-performance antireflective(AR)coatings to alleviate the abrupt change of the refractive indices is extremely important.Sol-gel SiO2 AR coatings have been the best choice for optical components in the high-power laser device because of their good AR and anti-laser damage performance.Although the conventional SiO2 AR coatings have been well-developed,with the increasing demand for the laser transmission efficiency,there are still some technical problems such as the lack of ultralow refractive index coatings,poor environmental stability and poor performance of broadband AR coatings to be solved.Based on the deep understanding of the antireflection principle and microstructure of coatings,a series of monolayer SiO2 AR coatings with low refractive index,good environmental stability,and gradient refractive index broadband double-layer SiO2 AR coatings were designed and prepared.The relevant research contents are as follows:(1)Fabrication of antireflective coatings with solid SiO2 nanoparticlesThe particle size and morphology control of the sol-gel SiO2 nanoparticles were achieved through Hexamethyldisilazane(HMDS)modification,and SiO2 monolayers with excellent optical properties and good environmental stability were successfully prepared.The results show that the refractive indices of AR coatings can be adjusted within a large range of 1.12-1.44;the transmittance of the coatings is improved by 6%or more,indicating its good AR performance;the highest water contact angle is up to 155°.The mechanism of the adjustability of the refractive indices of AR coatings was discussed.It is found that the surface energy effect of nanoparticles and the size effect of nanoparticles are important factors to reduce the refractive indices of AR coatings.The microstructures and macroscopic properties of the coatings were controlled by regulating the morphology and size of the nanoparticles.(2)In-situ modification of hollow SiO2 nanoparticles and preparation of antireflective coatingsIn order to solve the problem that the refractive index of the coatings prepared by conventional sol-gel method can not be reduced to below 1.10,hollow SiO2 nanoparticles(HSNs)were prepared by sol-gel method using polyacrylic acid(PAA)as template,and HSNs were modified in situ with HMDS.AR coatings with ultralow refractive index,superhydrophobicity were prepared using modified HSNs as the building unit.The results show that the organic modified HSNs can further reduce the refractive index of the coatings.Under the mild conditions,the refractive index of the coatings is reduced to below 1.10(as low as 1.08).In-situ modification of HSNs can significantly improve the resistance of vacuum to pollution of dimethyl silicone oil and improve the environmental stability of AR coating.(3)Morphology control of hollow SiO2 nanoparticles and preparation of antireflection coatingsUsing PAA as template,TEOS as precursors,methyl triethoxysilane(MTES)and polydimethylsiloxane(PDMS)as the modifier,by adjusting the ratio of related materials,feeding sequence and optimization process,a new kind of HSNs with spherical,honeycomb,tadpole and other morphologies were obtained by a one-step precess.These HSNs were used as the building unit to obtain the AR coatings.The relationship between the microstructure and the properties of the coatings shows that the refractive indices can be tuned between 1.038-1.18 by the size effect of the nanoparticle,the surface energy effect of the nanoparticle and the filling effect.Through the regulation of HSNs morphology,a simple and effective new method for the preparation of ultralow refractive index AR coatings has been developed,which provides a new idea for coating refractive index regulation and its environmental stability improvement.(4)Broadband gradient refractive index double-layer SiO2 antireflective coatingsThe upper layer with the refractive index of 1.16 was prepared from in-situ HMDS-modified SiO2 nanoparticles,and the bottom layer with the refractive index of 1.27 was prepared from acid/base-catalyzed composite SiO2 nanoparticles.Finally,a broadband double-layer coating was obtained successfully.The results show that the transmittance of the double-layer AR coating is 99.6%,98.0%and 99.3%at 351 nm,527 nm and 1053 nm,respectively;the double-layer SiO2 AR coating has excellent vacuum pollution resistance.The laser damage threshold is 23.6±1.1 J.cm-2,which is equivalent to that of monolayer SiO2 coatings prepared by Stober method.In this work,we have solved the problems of the current double-layer AR coating with poor AR performance and over-thick upper layer.The method has laid a solid foundation for the preparation of a broadband double-layer SiO2 AR coating with high transmittance,good environmental stability and high laser damage threshold.