Research On The Laser Induced Damage Threshold Variation In The Inhomogeneous Antireflection Films

Optical antireflection films are one of the most important components in laser systems.Increasing the laser induced damage threshold of the antireflection films has become a hot spot.The inhomogeneous films can improve the laser induced damage threshold and achieve broadband antireflection.The inhomogeneous films prepared by PECVD have the unique advantages of large continuous refractive index variation range and high manufacturing precision.In recent years,it has shown great application potential in the frontier research of laser films.This paper focuses on the variation between the inhomogeneous antireflection films and the laser induced damage threshold.Firstly,the different antireflection films are designed and optimized by simulation technology.The relationship between the variation of the inhomogeneous films and the electric field intensity is theoretically analyzed.Secondly,Different inhomogeneous antireflection films(multilayer gradient films and corresponding slope inhomogeneous films)are deposited on K9 glass by PECVD,so that the average transmittance of the samples is not less than 99%at the wavelengths 450～750nm.Finally,the variation of laser induced damage threshold of different inhomogeneous antireflection films is studied.The main results are as follows:(1)By selecting the appropriate basic antireflection films and combining certain optimization methods,three kinds of inhomogeneous antireflection films meeting the design requirements are obtained.Inhomogeneous film 1:G/H1→H/L/A,Inhomogeneous film 2:G/0.48H2/L1→H/1.31Li/A,Inhomogeneous film 3:G/Li/L/H3→H/Li/A,where nL=1.46,nL1=1.4,nH=1.96,nH1=1.7,nH2=1.85,nH3=1.75.The average transmittance of the three inhomogeneous films in the design band is 99.44%,99.28%,and 99.60%,respectively.(2)Three inhomogeneous films are prepared by the gradient method and the slope method.A variety of graded-index films and slope inhomogeneous films have been obtained that satisfy optical properties.The average transmittance of the graded-index films samples is between 99.02 and 99.41%,and the average transmittance of the slope inhomogeneous films samples is between 99.03 and 99.52%.(3)Under the premise that the target transmittance and the total optical thickness of the films are constant,compared with the basic films,the inhomogeneous films have a significant improvement in LIDT.For the same inhomogeneous film,under the same preparation conditions(gradient method and slope method),as the number of gradient layers increases,the LIDT of the films decreases.For the same inhomogeneous film,under the same film layer,the LIDT of the sample prepared by the slope method is higher than that of the sample prepared by the gradient method.For different inhomogeneous film,under the same film layer and the same preparation conditions,the most powerful laser damage capability is G/H1→H/L/A,in which the laser induced damage threshold of slope film 1-5 is 25.OJ/cm2 at the maximum,G/0.48H2/L1→H/1.3 1L1/A followed,and G/L1/L/H34H/L1/A is the weakest.