Preparation Of Broadband High Transmittance Silica Performance Research Preparation Of High Transmittance Silica Sol-gel Film Sol-gel Film And Application Performance Research

The application of antireflection coatings on transmission optical elements has significantly enhanced the optical performance of optical systems and expanded the application fields of optical systems.At present,the peak transmittance of single-layer antireflection coatings in the range of 640nm-660nm band is nearly 100%.For the monolayer anti-reflection film with a wide band of 700nm-900nm or even more,it still needs to be further explored and studied.Due to high transmittance,adjustable structure and high abrasive resistance,the SiO2 sol-gel film prepared by the sol-gel method has attracted people’s attention.With the development of the application,new requirements are put forward on the stability of sol-gel material,environmental stability and mechanical properties of sol-gel film with wide-band and high-transmissibility during preparation and use.Based on these new requirements mentioned above,the process and application of three traditional sol-gel methods for the preparation of SiO2 sol-gel films havebeen studied.On the basis of deeply understanding the catalytic principles respectively,the factors and laws affecting the viscosity and stability of SiO2 sol-gel have been studied.Possible methods and technical approaches to control the mechanical properties,refractive index and environmental stability of SiO2 sol-gel film have been explored,and the development and performance testing of wide-band anti-reflection film have been carried out thereupon.The relevant research results are as follows:(1)The factors affecting the viscosity and refractive index of SiO2 sol-gel obtained by acid catalysis has been studied by orthogonal experiments.The results show that among all the components of SiO2 sol-gel prepared by acid catalysis,anhydrous ethanol has the greatest influence on the sol-gel viscosity;When the viscosity is greater than 1.303 mPa.s,sol-gel is suitable for coating film,that is,the surface of the coated film is flat without defects.Dilution with absolute ethanol,ultrasonic-assist and adjustment of PH by adding hydrochloric acid(i.e HCl)can affect the viscosity of SiO2 sol-gel prepared by alkaline catalysis.The viscosity gradually decreases with the increase of the dilution ratio.The viscosity increases with the increase of ultrasonic-assisted time.With the addition of HCl,the sol-gel PH decreases and the viscosity increases.Only when the viscosity of SiO2 sol-gel prepared by alkali catalysis reaches～1.45 mPa.s,can it be applied to coating.(2)Exploring ways to improve the stability of SiO2 sol-gel prepared by alkali-catalysis,extend its usage time and the corresponding technological conditions.The experimental results show that:with the increase of the dilution ratio of anhydrousethanol,the sol-gel stability period is lengthened.the stability of sol-gel is also affected when the PH of sol-gel is changed by adding HCl.When PH=5,the sol-gel stable period is extended from 48h to 700h,but when PH=3,the stable period is reduced to～125h.(3)An experimental study on the mechanical properties of SiO2 sol-gel films has been carried out.The results show that:The SiO2 sol-gel film exhibits tensile stress.Residual stress increases with film thickness;and the residual stress increased;however,the stress difference between films of the same thickness decreases with the increase of film thickness;and it is found that the stress of film of the same thickness with the increase of annealing temperature.(4)Research on the refractive index adjustment method of SiO2 sol-gel film has been done.The refractive index of the film has been adjusted etween 1.1726 and 1.4136 by acid-base composite catalysis.trying to adjust and control the refractive index of SiO2 sol-gel film by changing the sol-gel ultrasonic-assisted time.(5)Carry out research on methods and technical approaches of improving the environmental stability of SiO2 sol-gel film explore the relationship between the environmental stability and the surface roughness of the film.It is found that the surface roughness of the film is smaller and the environmental stability of the corresponding film is higher.The modification experiments of SiO2 sol-gel film has showed that the environmental stability of SiO2 sol-gel film can be improved by HMDS immersion combined with assisted ultrasound.(6)The preparation of single-layer broadband SiO2 sol-gel film with refractive index of 1.23 and film thickness of 105nm was completed on the K9 substrate,and the average transmittance of 580nm-1000nm band and 700nm-900nm band is 97.82%and 98.05%respectively.