Research On Ion Beam Assisted Deposition And Post-processing Technology Of Laser Thin Film

Thin film device is one of the important components in laser systems.The excellent quality and performance is the key to ensure the normal operation of the laser system.Ion beam assisted deposition is a kind of technology based on the vacuum thermal evaporation.It has been widely used in the preparation of laser thin films.The influence of ion beams on film characteristics at various stages of film growth was investigated in this paper.Pre-deposition,during deposition and post-deposition,the substrate or film was bombarded with an ion beam:(1)Pre-deposition,the effect of ion beam on film characteristics by substrate cleaning was studied;(2)during the deposition process,the relationship between optical,laser damage characteristics and ion energy,film formation environment were investigated;(3)Post-deposition,the effect of ion beam processing on film quality was studied;(4)The influence of experimental parameters on properties of films by designing,preparing and post-processing a narrow-band pass filter.The results indicate:1)The refractive index of the subsequent deposited film is low at long substrate cleaning time before deposition,and the surface roughness Ra increases from 0.78 nm to 0.79 nm after cleaning.The refractive index of the film increases and the surface roughness decreases with the thickness increases when the cleaning time is constant.When the ion energy used to clean the substrate is 1350 e V,the refractive index of the subsequent deposited film is increased from2.3671 to 2.4664(wavelength of 532 nm),and its Ra is reduced from 0.78 nm to 0.60 nm.The laser damage threshold of the film obtained by coating the substrate after ion beam cleaning can be increased by 3.8 times.2)During the deposition process by ion beam assistance,the refractive index of the film is closely related to the ion beam current density,ion energy and other factors.E xcessive energy bombardment decreases the refractive index of the film.The increase of the laser damage threshold of the film is affected by the ion energy.When the ion energy is 800 e V,the laser damage threshold of the film is 7.6 J/cm~2,which is 26.63%higher;but when the energy is 950e V,the laser damage threshold is 5.6 J/cm~2,which was 6.7%lower than that deposited without beam assistance.Through investigating the film properties under different pressure,it is found that under high pressure,the refractive index and laser damage threshold of films deposited with various ion energies are generally low.By testing the surface roughness Ra of the films which deposited at 80°C,140°C,and 180°C respectively,it was found that with the deposition temperature increasing,the Ra of the film increases from 0.64 nm,0.76 nm to 1.66nm.The laser damage threshold of the film is high;the highest one is 8.8J/cm~2.3)The refractive index of the film can be increased by ion beam post-processing.Under high-energy ion bombardment,the surface roughness of the film is significantly reduced,which can be reduced to 1.12 nm.It is found that the ion source grid material affects the quality of the film.After replacing the molybdenum grid with aluminum grid,the surface roughness Ra of the film reduces to 1.07 nm.Ion beam post-treatment can improve the laser damage of the film by using an aluminum grid.The threshold value is increased up to 9.1 J/cm~2.Compared with laser post-processing,it is found that ion beam post-processing is more conducive to increasing the laser damage threshold of the film,and laser post-processing is more conducive to reducing the surface roughness of the film.When the laser irradiation energy is 4.8 m J,the surface roughness of the film Ra can be reduced to 0.43 nm.4)A filter with the film structure of G|(HL)~2H2LH(LH)~2L(HL)~2H2LH(LH)~2|A was prepared by ion beam assisted deposition.The peak transmittance of the film is 74.95%(1038nm).Through the ion beam post-processing,the transmittance of the filter is not improved,but the peak value is shifted to the long wave direction by 5 nm.The ion beam post-processing can increase the laser damage threshold of the filter by 15.44%.At the same time,it was found that the ion-assisted deposition of the filter film has high firmness and is not easy to fall off.