Study On Anti-scattering Characteristics Of SiO₂ Films By Electron Beam Evaporation

With the rapid development of modern high-power lasers and precision instruments,higher requirements are put forward for the performance of low scattering loss of optical thin films.SiO₂ is the most commonly used low refractive index material for high power optical films,and it can be combined with a variety of high refractive index materials to meet different spectral requirements.The study of the scattering properties of SiO₂ is important to deposit high precision optical thin films with low scattering loss.In this paper,we studied the scattering characteristics of single SiO₂ layers of electron beam thermal evaporation,and those of multilayers of SiO₂ and high refractive index compositions,taking the 1064nm band-pass filter deposited by SiO₂/TiO₂ as an example.The final goal of this paper is to provide theoretical basis and technical support for the development of low scattering loss thin films.The electron beam thermal evaporation technology was used under different substrate roughness,deposition rate,ion beam energy and oxygen partial pressure conditions to deposit single SiO₂ layers,to study effects of different processes on the surface roughness and scattering of SiO₂ thin films,and to analyze the process conditions to reduce the scattering.In order to explore the influence of mixed materials on the scattering characteristics of the film,we deposited Si-Al-O mixed film by co-evaporating SiO₂ and Al₂O₃.By comparing the roughness and scattering of the mixed film and single layer SiO₂ and Al₂O₃ film,we also analyzed the influence of the microscopic growth mode of the film on the scattering of the film.Taking SiO₂/TiO₂ combined band-pass filter as an example,we studied the effect of scattering loss of SiO₂ thin film on the spectrum of multilayer film and the process conditions of scattering reduction.We designed a band pass filter with low scattering loss by analyzing the multilayer electric field intensity characteristics.By studying the scattering characteristics of TiO₂ thin films,we deposited the TiO₂ anti-scattering thin films and deposited the multilayer films on the K9 substrate under the same roughness of electron beam evaporation.By analyzing the scattering mechanism of the multilayer of the roughness,film cross section and integral scattering test,we deposited the band-pass filter films with the same oxygen partial pressure and different oxygen partial pressure,and by lowering the scattering loss at the interface of TiO₂/SiO₂ multilayer,we deposited the 1064nm band-pass filter films using the method of equilibrium oxygen of partial pressure.Based on the scalar scattering theory,we fitted the transmittance of multilayer films deposited by two different processes mentioned above,using the calculation formulas of transmittance of multilayer films in the case of correlation and uncorrelation scattering.To verify the fitting results of the theoretical calculated curve and the actual measured spectral curve,we used an integrating sphere After optimization to test the integrated scattering.After the optimization,the average transmittance of double-sided band-pass filter film of 1040-1090nm is 95.5%,the transmittance at 1064nm is 96.5%,and the average transmittance at400-1025nm and 1105-1300nm are 0.18%and 0.25%,meeting the designing criteria.