Research On Athermal Optical Design Method Considering Thermal-Induced Surface Deformation

Optical instruments,whether for commercial lenses or military aircraft applications,require satisfying and stable optical performance over a wide temperature range.With the widespread use of plastic materials and the increasing sensitivity of optical systems to temperature,the degradation of optical performance caused by thermal-induced surface deformation has become a problem in the field of athermalization.Although structure-thermal-optical performance integrated analysis(STOP)can be effective in reducing thermal-induced surface deformation,the multidisciplinary design and analysis process is cumbersome and complex,and compensation methods are usually through costly thermal control design or structural optimization.In this paper,we propose two optical design methods to eliminate thermal-induced surface deformation for two typical types of temperature distributions optical systems.For the optical systems with uniform temperature distribution,this paper proposes an optical optimization approach that optical designers can complete independently in terms of passive athermal optical design considering thermal-induced surface deformation.For the optical system with non-uniform temperature distribution,this paper proposes an optical optimisation plus focusing compensation method to achieve thermal compensation design considering thermal-induced surface deformation,by taking the high-energy laser pointing optical system as an example.The main research contents of this paper are as follows:1.Basic theoretical research on athermal optical design considering thermalinduced surface deformation.Firstly,theoretical analysis of the temperature effect on the optical system parameters is carried out,which indicates the inaccuracy of the lens interval thermal analysis results because the conventional optical design software is unable to characterise the assembly information between the lenses.At the same time,the STOP integrated analysis often requires multiple iterations by engineers with different professional backgrounds,making the whole process time-consuming and labour-intensive due to multi-disciplinary interaction and cross-disciplinary communication efficiency issues.Then,theoretical analysis of the thermal-induced stress effect shows that the thermal stress on the lens is only related to the assembly parameters of that lens itself and not to the overall structure of the lens barrel.A wide range temperature passive athermal optical system is used as an example to simulate the effect of the thermal-induced surface deformation on the imaging quality of the optical system.Finally,the optical optimizability of the thermal-induced surface deformation is analyzed theoretically.2.Passive athermal optical design method considering thermal-induced surface deformation.First,the overall design process of the passive athermal optical design method considering thermal-induced surface deformation is introduced.The thermal analysis method and program implementation process in optical design software considering inter-lens assembly method are focused on.And how to characterize the thermal-induced surface deformation in optical design software by parametric finite element analysis(FEA)and self-programmed Zernike polynomial fitting macro is presented.Then,the optical passive athermal design example considering thermalinduced surface deformation is demonstrated and validated,and the optimization results show that the method is feasible.Finally,the simulation results of parametric FEA and Zernike polynomial fitting are shown to be consistent with the actual surface deformation in terms of trend by the single-lens low-temperature surface interference experiments.3.Design of high-energy laser pointing optical system considering thermal-induced surface deformation.Different from the athermal design of the thermally stable environment,the lens becomes a gradient temperature field distribution when the highenergy laser irradiates.The optical design method brings the gradient temperature distribution and thermal-induced surface deformation into the multi-round iterative optical optimization design by means of multi-physics field FEA and Zernike polynomial fitting,so that the high-energy laser optical system can still have good farfield focusing characteristics in the laser irradiation state.In this thesis,the shortcomings of the conventional athermal design method are firstly presented,and from the perspective of optical designers,the optimization method enables the optical designers complete independently in terms of athermal optical design considering thermal-induced surface deformation.The proposed athermal design method is verified to be feasible for two types of optical systems in different thermal environments.