Research On Optical And Mechanical Structure And Integration Technology Of Atmospheric Dispersion Corrector For Wide-field Optical Spectrometer

In the process of light passing through the atmosphere to the optical instrument,the atmosphere will produce dispersion effect on different wavelengths of light,which will affect the optical performance of the spectrometer.In order to ensure the image quality,atmospheric dispersion corrector can be used to compensate atmospheric dispersion.The Thirty Meter Telescope(TMT),a large international collaboration of countries and institutions,is one of a new generation of very large aperture telescopes being built internationally,carrying a wide range of scientific instruments.The Wide-Field Optical Spectrometer(WFOS)is one of the four instruments that are being built and put into use on the first priority of TMT.To ensure the imaging quality of WFOS,a linear atmo-spheric dispersion corrector(LADC)is carried out for the front optical path of WFOS.The LADC is located in front of the WFOS and compensates the atmospheric disper-sion before the light enters the WFOS.In this dissertation,the optical and mechanical structure of WFOS LADC is studied.Firstly,the key optical component of LADC,the large aperture wedge prism,is supported reliably,based on of witch,the complete struc-ture design of LADC is completed.Then the structural design of LADC is evaluated and optimized based on the optical,mechanical and thermal integrated simulation analysis and optimization technology.The specific work of this dissertation is as follows:Based on a lot of research on the support methods of large aperture mirrors,the differences between the working modes of mirrors and prisms are compared in detail.For the large aperture wedge prism studied in this dissertation,the mechanism of op-tical surface change caused by the support system is explored by analyzing the force transfer process of the large aperture wedge prism with non-uniform cross-section in the body element under the action of gravity and the force of the non-rotationally sym-metric mirror body in the rotation process when the optical axis is horizontal.Based on the in-depth study of the structure,working mode and deformation mechanism of the large aperture wedge refraction prism in this dissertation,a six-point support scheme aiming at the support point of LADC non-rotationally symmetric large aperture wedge refraction prism passing through the prism center of gravity is proposed.The optical surface deformation caused by different distribution of gravity and support force is an-alyzed in detail,and the Root Mean Square(RMS)of optical surface deformation of prism under different support schemes and different working conditions is compared.RMS is used as the evaluation index to select the design method.Through multi-angle comparison,the superiority of the proposed scheme based on the large-aperture optical surface deformation mechanism is verified.The evaluation,comparison and optimization of LADC design schemes need to involve the cross and integration of multiple disciplines of Mechanics,Optics and Ther-mal.In this dissertation,the optical-mechanical-thermal integrated analysis and optimization platform is built.Firstly,the theoretical bridge connecting different disci-plines of optical,mechanical and thermal is studied,and then an interface program is written through the multi-software integration platform to connect the analysis tools of various disciplines to form an integrated analysis loop,so as to realize the automatic transmission of design parameters in the analysis loops.For the objects to be analyzed and optimized,digital modeling,finite element analysis,result data processing,model upgrading and optimization are carried out by using design and analysis software of various disciplines,which improves the optimization efficiency of optical,mechanical and thermal integrated analysis.The optimization results of the support system of two sub-components of LADC show that,for the prism 1 component,in the range of operat-ing temperature[2°C,42°C],under the low limit temperature 2°C coupling with gravity and the high limit temperature 42°C coupling with gravity,the RMS of optical surface deformation were optimized from 103.74nm and 110.46nm to 63.14nm and 47.86nm,and the decrease of optical surface deformation reached 39.1%and 56.7%,respectively.For prism 2,the RMS of optical surface deformation is optimized from 154.99nm and289.13nm to 78.56nm and 108.45nm,respectively,at the low limit temperature 2°C and the high limit temperature 42°C coupling with gravity.The decreases are 49.3%and62.5%respectively,which meet the design requirements of optical surface deformation less than 158nm.The structure dynamics of LADC optical system is analyzed.Firstly,the modal analysis of two cantilever support frames of LADC is carried out to ensure that they have sufficient natural frequencies and will not be excited by internal and external dynamic loads.In addition,since TMT is located in a zone with frequent seismic activities,in order to ensure that LADC will not suffer unbearable damage in an earthquake,seismic impact analysis is carried out.Taking the seismic design response spectrum of the location of TMT as the loading condition,the seismic analysis of LADC under 200-year return period and 1000-year return period earthquakes is carried out respectively.The analysis results show that the current design is safe under the two seismic design response spectrum conditions of TMT.The research method of large aperture optical precision instruments proposed in this dissertation is also applicable to other optical precision instruments,especially for the support design of large aperture transmission optical elements.