空间引力波探测望远镜光学系统设计

Optical design of space gravitational wave detection telescope

在空间引力波探测中,望远镜是空间激光干涉测量系统的重要组成部分,其出瞳处波前误差与抖动光程(Tilt-ToLength,TTL)噪声间的耦合,是影响空间引力波探测的主要噪声源。首先,基于平顶光束与高斯光束的干涉模型,采用Fringe Zernike多项式表征望远镜出瞳处的波前误差,运用LISA Pathfinder(LPF)信号分析出瞳处波前误差与TTL噪声的耦合机理。其次,采用蒙特卡洛分析方法,研究不同数值波前误差下低阶像差占比对TTL耦合噪声的影响,确定了不同数值波前误差下,望远镜光学系统出瞳处满足TTL耦合噪声控制要求的低阶像差设计比例。最后,基于上述理论分析结果与像差控制要求,完成了空间引力波探测望远镜光学系统设计,望远镜入瞳直径为200 mm,出瞳处波前误差RMS值为0.01908λ,低阶像差占比不高于50%。分析结果表明,当光束抖动在±300μrad以内,TTL耦合噪声不超过8.25 pm/μrad;通过公差分析得知,TTL耦合噪声最大值为15.50 pm/μrad,满足空间引力波的探测要求。

In space gravitational wave detection,the telescope is an important part of the space laser interferometry system.The wavefront error at the exit pupil of the telescope is coupled with the Tilt-To-Length(TTL)noise,which becomes the main source of noise in space gravitational wave detection.Firstly,based on the interference model between a flat-top beam and a Gaussian beam,the Fringe Zernike polynomial is used to characterize the wavefront error at the exit pupil of the telescope,and the LISA Pathfinder(LPF)signal is used to analyze the coupling mechanism of the wavefront error at the exit pupil and the TTL noise.Secondly,the Monte Carlo analysis method is used to study the influence of the proportion of low-order aberrations on the TTL coupling noise under different numerical wavefront errors,and determine the low-order aberration proportions which meets the requirements of TTL coupling noise control at the exit pupil in the design of the telescope optical system under different numerical wavefront errors.Finally,based on the above theoretical analysis results and the aberration control requirements,the optical design of the space gravitational wave detection telescope is completed.The diameter of the entrance pupil of the telescope is 200 mm,and the RMS value of the wavefront error at the exit pupil is 0.01908λ.The proportion of low-order aberrations is not higher than 50%.The analysis results show that the TTL coupling noise does not exceed 8.25 pm/μrad when the beam jitter is within±300μrad.Through tolerance analysis,the maximum TTL coupling noise is determined to be 15.50 pm/μrad,which meets the requirements of space gravitational wave detection.