Design And Preparation Of Infrared Thin Films For Laser Protection

With the development of high power and high energy laser systems, the optical films components exposing to long-term high energy laser irradiation are facing with increasing threats, so it is more and more important to produce laser protective films. In order to enhance the laser induced damage properties of optical films components, besides advanced methods and processes, post-treatment is also important to improve the laser induced damage threshold (LIDT)of thin films.In this paper, at first. ZnSe. BaF2monolayer films were deposited on double-side polished Si and K9glass substrates by thermal evaporation techniques, the influence of preparation process parameters and laser post-processing on laser damage properties was investigated, respectively. The results showed that the laser induced damage threshold (LIDT) of the films can be increased effectively by certain dosage of laser irradiation, the LIDT of ZnSe films was8.2J/cm2and BaF2films was22.5J/cm2after pretreatment.Secondly, the laser protective films stack (1064nmHR/3～5μmAR) on infrared window was designed according to optimization of standing wave field distribution successfully. The maximum electric field of the films with the stack of G|0.44H0.26L2.9H1.4LHLHLH0.51L1.28H1.45L0.44H2L|A was in BaF2films with stronger laser protective capability, thus reduction the electric field strength at the interface effectively. The films were deposited by using a ZZS500-2/G-box-type vacuum coating machine, and then the as-deposited thin films were undertaken by laser pretreatment and annealing treatment, respectively. The LIDT of thin films can approach4.7J/cm2after the optimal laser pretreatment with energy density2.3J/cm2The LIDT of thin films can approach6.2J/cm2after the optimal annealing treatment with temperature250℃Then, the laser damage properties of3～5μm conventional AR films with the structure of G|HL|A were investigated. The films were treated by laser pretreatment and annealing treatment, respectively. The LIDT of thin films can approach5.2J/cm2after the optimal laser pretreatment with energy density2.4J/cm2. The LIDT of thin films can approach6.3J/cm2after the optimal annealing treatment with temperature250℃At last, the above two film stacks were deposited at two sides of Si substrates. The measure results showed that the reflectivity of the sample was more than98.4%at1064nm, the average transmissivity can approach96.8%and the peak transmissivity can approach98.5%at3～5μm. Thus the results meet the demand of design.