Research On Opto-mechanical Design And Stray Light Analysis Method For Space Gravitational Wave Detection Telescope

Space gravitational wave detection Taiji plan uses the Michelson interferometry principle to build a very long baseline laser interferometric gravitational wave detector.Through the precise measurement of the position change between the test masses at both ends of the very long baseline,it can realize the detection of gravitational wave signals.Its ultimate goal is to achieve the detection of gravitational wave signals with pm resolution in the frequency range of 0.1 m Hz to 1 Hz.The space gravitational wave detection telescope is one of the key technologies of space gravitational wave detection and is the core of the laser interferometric gravitational wave detector to build a very long baseline(3 million kilometers).For the space gravitational wave detection telescope,there are two core technical problems to achieve such high detection accuracy under the very long baseline: first,the optical and mechanical structure of the telescope needs to meet the strict requirements of ultra-high detection resolution on the stability of the interference link,especially the size stability of the telescope;Second,the interference arm length of 3million kilometers leads to the extreme signal-to-noise ratio of the laser interference link,which requires the telescope to meet the extremely low stray light requirements.In order to achieve the breakthrough of the above two technical problems,it is necessary to conduct a comprehensive and systematic study on the design of the optical mechanism of the telescope,the measurement of the dimensional stability,and the accurate stray light analysis.The main research work of this paper is as follows:First,the index data of each system of the space gravitational wave detection telescope prototype were determined.Through the simulation analysis of the off-axis four-inversion optical system,the rationality of the existing optical design scheme is clarified,and the index assignment of the optical system is completed based on the results of the tolerance analysis.At the same time,the study of the influence mechanism of the backward scattered stray light from the telescope on the phase measurement was carried out,the engineering analysis index of stray light(PST)was obtained,and the control requirements of the roughness of each optical surface and environmental cleanliness of the telescope were proposed based on the index.Then,the overall design of the space gravitational wave detection telescope is determined and the detailed optimization design of the optical machine structure is studied.In this paper,a lightweight design method based on the three-dimensional equivalent stiffness model is proposed,and the full parametric modeling of the lightweight mirror model is completed.The simulation results show that the error rate of the 3D equivalent stiffness model is within 12% compared with the detailed modeling,which can well reflect the structural characteristics of the lightweight telescope.Meanwhile,based on the flexibility theory,the design of the flexible structure of the main mirror is completed by using the parametric modeling method by combining the requirements of gravity,assembly error,and fundamental frequency on the support flexibility.In addition,based on the design method of topology optimization and parameter optimization,the design of Invar type and SiC type main support frame of the telescope was completed.Furthermore,the Invar telescope and the SiC main support frame were built and tested for routine performance.The results show that the first-order free mode frequency of the Invar telescope is 228 Hz,and the wavefront error RMS at the exit pupil is 76 nm,while the first-order free mode frequency of the SiC main support frame is 504 Hz.The dimensional stability test system based on the heterodyne interference principle and the homodyne interference principle was built.The dimensional stability tests were conducted at room temperature on the Invar-type and SiC-type main support frames,which have the greatest influence on the optical range stability of the telescope,respectively.The reliability of the numerical model of the SiC-type main support frame was verified by using the test data.The predicted dimensional stability of the SiC-type main support frame in orbit was obtained in combination with the space thermal environment analysis,which showed that the dimensional temperature was better than1 pm/Hz1/2 when the frequency range of temperature fluctuation was in the interval of[20 m Hz,1 Hz].Finally,the effective frequency band of the scattering from the optical surface roughness of each reflector was studied and the optical surface roughness of each was actually measured.Meanwhile,the systematic PST value(2.86×10-7)of the Invar-type telescope in the existing processing state was analyzed with the help of a stray light analysis model.And the phase noise(38.0765 pm)was obtained by conversion.In addition,the BSDF model of the optical surface after damage by micrometeorites was established based on the damage equation and Peterson scratch model.The prediction of the stray light performance change of the telescope in orbit was realized,and the results showed that the level of PST change of the telescope does not exceed 5×10-12 during its 10 years of service.The research content of this paper aims at the two key technologies of the space gravitational wave detection telescope,comprehensively considering the wavefront error,size stability,and stray light level of the telescope.Through the actual test of the prototype,the feasibility of the related technologies is largely verified.For the research of space gravitational wave detection telescope,this paper has extensive reference significance and reference value.