| Aero-optical effect is one of the important factors that affect the optical system imaging quality.Gas will produce density change when it flows or disturbs by external environment and lead to changes in the refractive index of medium because of the gas medium compressibility.Especially in high speed flow field,the density variations tend to have an enormous discrepancy.When the beam propagates in this non-uniform refractive medium,deflection,jitter and phase change will occur,which will affect the beam quality.The research of aero-optic suppression method can reduce the influence of aero-optic to a certain extent.At the same time,it can provide guidance for optical system design,suppression and correction of system difference.It has high value for scientific research and practical applicationAccording to different application environments,this paper is divided into three parts to study the methods of suppressing the aero-optical effects of optical systems.The first part is the application research of the large aperture optical window.The second part is the research of the suppression method of the aerodynamic optical effect of the flow field in the beam expanding system.And the third part is the research of the aerodynamic optical effect of the high-speed outflow field.For the optical system in complex application environment,the optical window is an important means to protect the stability of the internal environment of the optical system and isolate the interaction between internal and external environment.The first part of this paper takes the large aperture optical window as the research object,and discusses the application of the optical window in the large aperture optical system from the aspects of the model building,material selection,force analysis,structure design,processing technology and supporting technology of the optical window.Aiming at the problem of supporting for large aperture optical window,this paper proposes the intermediate zonal auxiliary supporting based on traditional girth support,and analyzes the feasibility and supporting effect of this scheme from four aspects,such as optical window thickness,diameter-thickness ratio,blocking ratio and supporting structure mode.Taking the transmitted beam wavefront of the optical window as the evaluation index,the supporting effects of the traditional support form and the intermediate zonal auxiliary supporting are analyzed and compared,and the relationship between the transmitted beam wavefront and the thickness ratio of the aperture of the window is established.For some of the large diameter beam expanding system which is not suitable for solid state window sealing,this paper designs and improves the air inlet layout of the purification device of the beam expanding system.Through flow field analysis combined with ray tracing method of variable refractive index medium,a complete set of methods for analyzing aero-optical effects are summarized in this paper.In the process of simulation analysis,the main research ideas,including semi-empirical design-flow field simulation-flow field structure analysis-stream-optical coupling-image quality evaluation-structure improvement,were adopted to improve the intake air layout of the beam expanding system through flow field structure analysis and optical image quality evaluation results.In the end,we designed the 16×360 matrix forms of the intake layout holes.The wavefront error RMS value of the beam passing through the beam expanding system to the primary mirror due to the aerodynamic optical effect of the flow field in the beam expanding system under the intake state is only 3.2×10-2?m,less than ?/20,and it is less than that in the process of expanded beam ray tracing system In order to capture the aero-optical effect of the mutation region in the ray tracing process of the beam expanding system,the gradient index ray tracing method with step size adjustment function based on local refractive index gradient is improved in this paper,and the variation of refractive index ?n is added as the discriminant condition.In order to verify the research process and results of the analysis,in this paper,the flow field in the 850 mm beam expander system has carried on the experiment,the experiment scheme adopts 16×360 air inlet to inflatable beam expander system,matrix structure and the flow field in the beam expander system and beam were measured through the expanded beam system,finally the experimental results and the simulation analysis results of the error is within 10%.For high-speed flow field,the structure of the outflow field and the effect of the flow field on the beam quality of the conformal optical window in different states are analyzed in this paper with a hemispherical optical head of 200mm diameter as the research object.A ray tracing method based on step length of refractive index is proposed in the process of ray tracing in an outflow field containing shock waves.In the ray tracing process,the refractive index step is used instead of the geometric step,and the step size can be adjusted adaptively. |
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