Study On Influence Of Wide Temperature Range On The Performance Of Deformable Mirror

Since the traditional adaptive optics(AO)system is installed in the Coude room below the telescope,so the light from the stars are reflected by a series of mirrors,and then enter the Coude room.Thus,the complexity of the system will increase and the light we captured will become darker.If we use AO system to replace these mirrors,then the complexity of the system will decrease and the brightness of imaging spot will increase.In this case,the performance of the AO system is affected by the ambient temperature,in particular the aberration correction capability of the deformable mirror.As the telescope generally work at night,so the adaptive optical system operating temperature changes with the four seasons,and the minimum temperature is-10?,max temperature is 20?.Generally,the operating temperature of optical instruments in AO system is room temperature,so the performance of optical instruments in the low temperature needs to be studied,especially the deformable mirror(DM)which is the core device of the AO system.The research of low temperature deformation mirror is imperative.The AO system,low temperature AO system and DM are introduced;the research status of low temperature deformation mirror at home and abroad is analyzed.We can conclude that the two factors that influence the performance of low temperature DM are mirror surface deformation and the performance of the actuators at low temperature.In addition,the characteristics of the different structure of DMs at low temperature are analyzed.The discrete actuators continuous surface DM is selected to be the object of study.Theoretical method was used to analysis the main cause of the surface deformation of the discrete continuous surface DM at low temperature.It is come to be that the surface deformation of DM is caused by the mismatching coefficient of thermal expansion(CTE)between the actuators and the base induced base deformation.The surface deformation of facesheet and base of the 61-element ULE DM ware calculated through the finite element method(FEM),to verify the correctness of the theoretical analysis.On this basis,a new structure of the DM was proposed to solve this problem.The working principle of the optimized DM is explained theoretically.The surface deformation of facesheet and base of the optimized 61-element ULE DM ware calculated through the FEM.It was found that the optimized DM can effectively decrease the surface deformation of facesheet and base.The influence of actuator arrangement and faceshhet on the mirror deformation of two structural deformable mirrors at low temperature was analyzed.We can conclude that the optimized mirror was not affected by these factors.The surface deformation of ULE DM,the K4 DM,the optimized ULE DM and the optimized K4 DM at low temperature are calculated,to provide the theoretical basis for the next experiments.The two factors that affect the performance of the low temperature DM are the initial mirror surface deformation and the performance of actuators at low temperature;so we measured the low-temperature performance of the actuators firstly.The experiments results showed that the maximum deformation of the piezoelectric ceramic transducer(PZT)actuators between 20? and-60? is constant,indicating that the PZT actuators perform well between 20? to-60?.The surface deformation of four sample DMs(ULE DM,K4 DM,optimized ULE DM and optimized K4 DM)between 20 ? and-20 ? was measured.The experiments results showed that the surface deformation of DM increased as temperature decreased;the surface deformation of the K4 DM is smoother than that of the ULE DM at same temperature;the optimized DM can effectively reduce the surface deformation of DMs at low temperature,proving the correctness of the formerly theoretical study.The low temperature surface deformation of the two 913-element DMs(K4 DM and ULE DM)in diameter and in the ?150mm clear aperture were simulated and tested.The experiments results were consistent with the simulation results,which showed that the surface deformation of K4 DM is smoother than ULE DM at the same low temperature.And the direction of surface deformation of them is opposite.Among them,the surface deformation of K4 DM at low temperature is small enough,so the aberration correction capability of the AO system doesn't influence by the surface deformation of K4 DM.K4 DM satisfys the requirements of AO system.