Effect Of Post-treatment Process On The Properties Of Optical Films

With the development of laser technology,high-power lasers have attracted more and more attention.High-power lasers play an important role in industrial,military,and nuclear fusion.People have made great efforts to increase the output power of high-power laser systems.The optical film plays an important role in the laser system,but with the increase of the power of the laser system,the optical film is easily damaged at a high laser power density,which has become a bottleneck for increasing the power of the laser system.This paper focuses on the laser resistance of the film.The thermal annealing,ion post-treatment and two-step post-treatment methods are used to improve the nanosecond laser damage threshold(LIDT)of the optical film.The specific research contents are as follows:(1)The mechanism of the effect of Ar/O mixed plasma post-treatment on the optical properties and laser damage resistance of TiO2 single-layer films was studied.For the single-layer TiO2 film prepared by the electron beam evaporation technology(EBE),during the Ar/O mixed plasma post-treatment process,Ar ions can remove the surface defects of the film,and O ions can reduce the non-stoichiometric defects of the film material.The optical properties and laser damage threshold of TiO2 film were improved.Therefore,the optical characteristics and laser damage threshold of the TiO2 film are improved.The experimental results show that with the increase of plasma post-treatment time,the thin film density of the film increases,the surface roughness decreases,and the surface defect density decreases first and then increases.Under 1064nm laser radiation,the laser damage threshold(LIDT)of the TiO2 film increased from 5.6 J/cm~2 without plasma post-treatment to 9.65 J/cm~2 after 20-minute post-treatment,an increase of 72.3%.(2)A two-step post-treatment process combining thermal annealing and plasma post-treatment technology was proposed,and its influence on the HfO2 single-layer film was studied.Studies have shown that ion post-treatment can effectively reduce the surface defect density of films.Ion post-treatment can make the film smoother,remove shallow layers of impurities and nodules;thermal annealing can reduce the water vapor inside the film,and deep oxidation of the film reduces non-stoichiometric defects of the film.The combination of ion post-treatment and thermal annealing complements the advantages of both post-treatments and minimizes film defects.Therefore,the damage threshold of the HfO2 thin film sample after two-step post-processing was significantly improved.The laser damage threshold of the un-processed film was 7.4J/cm~2,and the laser damage threshold of the two-step post-processing film was 12.5 J/cm~2.(3)The effects of the two-step post-treatment method on the optical properties and LIDT of HfO2/TiO2/SiO2 high-reflection film were explored.Due to the increased plasma post-treatment process,compared with the simple thermal annealing post-treatment,the two-step post-treatment broadens the reflection bandwidth of the high-reflection film,significantly reduces the film surface defect density,and reduces the film's internal stress.At the same time,the two-step post-processing also effectively removed the surface defects of the highly reflective film,reduced the oxygen vacancies inside the film,and improved the internal electric field distribution of the film.Therefore,the laser damage threshold of the highly reflective film was further increased.The test results showed that the LIDT of HfO2/TiO2/SiO2 high reflective film after two steps reached 32.8J/cm~2,27.6%higher than that of the sample only after thermal annealing,and 110.3%higher than that of the sample without post-processing.