Research On Multi-wavelength Laser Films Deposited By Ion Beam Sputtering

With the development of tunable laser applications recently,it's put forward that the higher requirement for multi-wavelength laser films technology.Which mainly manifestes in two aspects:one is that the wider bandwidth of the high reflection films,and the other one is that the larger laser damage threshold of the films.Currently limited by the narrow bandwidth,it has to be relplaced the cavity mirror when the output wavelength of tunable laser is changed.And the damage threshold of the films on nonlinear crystal has become the bottleneck of restricting the improvement of output power.So,it's of great scientific significance and practical value to carry out theoretical and experimental research to broaden the bandwidth and enlarge the damage threshold of the multi-wavelength laser films,which will play a great role in promoting the development of tunable laser technology.The high-performance broadband mirror can only be realized by all dielectric film stacks.The films system designed by this method has the characteristics of many layers and large total physical thickness,which will lead to some problems such as the stress-induced surface distortion and the reflectivity depression caused by the local resonance amplification of absorption;multi-spectral antireflection film on crystal which has both anisotropies in optical and mechanical properties is mainly used in mid-infrared optical parametric oscillation laser and striked by high-power laser.For those kinds of reasons,the laser films element on nonlinear crystal is easily damaged,and has poor reliability property currently.In this paper,ion beam sputtering deposition technology and oxide film materials are chosed.Though ion beam sputtering oxide films have the advantages such as the high density and few defects,it will bring high-pressure stress problems.In addition,there are few reports on the characteristics and application of oxide films in mid-infrared.It aimes at the question of the optical constants accurately characterization of oxide films,Tauc-Lorentz and Cody-Lorentz composite dispersion model is used in this paper which is modified mainly emphasis on the band tail absorption attenuation.So as to the absorption across the inter band transition and the transparent region is more reasonable.The optical constants of Ta₂O₅ and Hf O₂ films are characterized by the modified composite dispersion model,and the results show that the fitting deviation is obviously reduced.Then the correlation is studied between optical and mechanical properties of oxide films,and the revealed rule can provide basis for process adjustment.Secondly,the effects of charge oxygen on the optical properties,microstructure and stress properties of Ta₂O₅,Hf O₂,Al₂O₃ and Si O₂ films are systematically studied to solve the problem of high-pressure stress state and micro-defects of oxide films prepared by ion beam sputtering.Simultaneously,the effects of different starting sputtering materials on the properties of Ta₂O₅ and Hf O₂ films are emphasis compared.The correlation between the properties of oxide films and process parameters is established.Especially,the optimal process for controlling oxygen defects is obtained which can reduce the damage risk caused by absorption induced by oxygen defect when films irradiated by laser.Then,it's established that the effects of annealing post-treatment on the energy band characteristics and optical characteristics in infrared band of oxide films,and the method of stress adjustment by annealing post-treatment is obtained.In particular,the new idea of post-processing is proposed which can introduce low thermal stress based on the pressure adjustment under the positive pressure background.The hot isostatic pressing method is employed for films which is used for the preparation of optical materials.Compared with the traditional post-processing method,the hot isostatic pressing method can greatly reduce the secondary thermal stress which is due to the difference of thermal expansion coefficients between the films and the substrate material.Finally,a film design method for ultra broadband mirror is studied to reduce the surface distortion caused by stress.In which equal thickness films are designed on both sides of the substrate.However,the stress of the films couldn't be reduced by this design method,it's necessary to select the low stress film preparation process parameters,and adopt hot isostatic pressing method after the film preparation to reduce the film stress to improve the reliability of the mirror.Lastly,the ultra broadband laser refection films are prepared with the results of average reflectivity of 99.91%in the range of 400-1200nm and surface figure of 0.072?.Focus on the problems of the design and preparation of mid-infrared antireflection films on nonlinear ZGP crystal,an optical-mechanics integrated design method is proposed which is based on adding matching layer of Al₂O₃ film to to solve the problem of poor mechanical stability caused by the anisotropy of thermal expansion coefficients in ZGP crystal.Simultaneously,the antireflection coating design method is proposed for the case of the substrate with anisotropy refractive index or the optical constants difficult to accurately calibrate.Lastly,the mid-infrared multi-spectra antireflection films on nonlinear crystal are prepared by ion beam sputtering,and the measured result shows that the laser damage threshold can reach 4J/cm².