Research On Co-Phasing Detection Technology Of Segment Telescope Based On Dual-Wavelength Interference Method

The astronomical telescope is an important tool for astronomical observation.With the development of space technology,the resolving ability of astronomical telescopes are becoming increasingly demanding.Increasing the aperture of the primary mirror is an effective means to increase the resolution of the system according to the Rayleigh criterion,but as the aperture of the primary mirror increases,the design,processing,fabrication,detection and other technologies of the telescope also face unprecedented challenges.As a result,segmented telescopes have emerged as one of the important directions for the future development of space-based large aperture telescopes due to their advantages such as low processing difficulty,easy transport,and not being limited by the size of the satellite fairing.At present,there have been some research achievements at home and abroad,including Keck Ⅰ,Keck Ⅱ,TMT,JWST and so on.But the spliced telescope also brings many new technical problems,such as the nonlinear increase of the complexity of assembly due to the increase of the segmented mirrors components;the diffraction effect is easy to appear in the edge and gap of the segmented mirrors and the detection of the co-phase error between the segmented mirrors.Only when the confocal and co-phase of the segmented primary mirror are realized can the segmented telescope achieve the same image quality as the single primary mirror.Therefore,in the design process,it is necessary to analyze the tolerances and various misalignments of each sub-mirrors of the segmented primary mirror,and realize the accurate detection and installation of the co-phase errors between the mirrors of the segmented mirror,so that the segmented telescope can realize the co-phase of each sub-mirrors,and the segmented telescope can be effectively put into use.To solve the problem of co-phasing error detection,there are a variety of research methods,each has its advantages and disadvantages.For example,the four-pyramid wavefront detection method has high detection accuracy but small range and difficult component processing.Dispersive fringe method has large range but low accuracy.The wide and narrow band Shaker Hartmann method achieves large range and high precision by combining the wide band method and narrow band method,but at the same time loses the real-time detection.In contrast,interference method has high precision,simple optical path and short detection time.If it can overcome the defect of small dynamic range,it will be able to solve the problem of common phase detection well.In this paper,we investigate the detection technique of co-phase errors in a segmented telescope system based on two-wavelength synchronous phase shift interferometry,which solves the bottleneck problem of small dynamic range of traditional interference methods and enables the detection of common phase errors with high accuracy and large dynamic range.The main research content of this paper is as follows:1.In the aspect of principle research,the principle derivation and model establishment of dual-wavelength synchronous phase-shifting interferometry are carried out,and the basic principle of using this method for co-phase detection is introduced.Moreover,various errors in the segmented system are simulated and analyzed to fully understand the influence of various errors on the detection results.The tolerance of the common-phase error is analyzed to provide guidance for the subsequent detection and adjustment of the common-phase error.2.The optical path of the dual wavelength synchronous phase shift interference system is designed,and the parameter requirements of each component of the dual wavelength interference system are analyzed.The construction and adjustment of the optical path are completed.The noise source of the interferometer is analyzed and removed.The interferometer is further optimized considering the requirements of the interferometer portability.3.In view of the problem of phase unwrapping algorithm,the research and comparison of common phase unwrapping algorithms such as pruning method,mass graph oriented method,Fourier transform method and minimum flow method were completed.Based on the least square method,the discrete cosine transform method was used to complete the algorithm writing.4.In view of phase unwrapping errors caused by wave front segmentation in continuous areas,the traditional solution has poor results for large errors or complex surface shapes,or it can only be calculated manually for some situation.In this paper,the minimization of Zernike gradient fitting residuals is raised and the algorithm has been written.Through simulation and experiment,it is verified that the method has a good solution effect for a variety of obstruction and complex surface shapes.5.In view of the error amplification effect of the synthetic wavelength results in dual-wavelength interference test,the principal component analysis method is used to study and write the relevant algorithm.The applicability and effectiveness of this algorithm for error amplification effect are verified by simulation.6.In terms of software operation platform,the software platform of dualwavelength synchronous phase-shifting interference system was established,and a variety of functions such as real-time display,Mask selection,face shape calculation,filtering,Zernike fitting and synthetic wavelength result calculation were designed and realized.7.In terms of experimental verification,experiments were designed and carried out for flat mirror,spherical step mirror and segmented system,and the high-precision detection ability of single wavelength of dual-wavelength interference system was verified by flat mirror test.The spherical step mirror test verifies the detection ability of dual-wavelength interference system with large piston error range.The detection of the segmented system systematically verifies the ability of the dual-wavelength interference system to detect piston errors and the functional applicability of the software platform.In this paper,the theoretical derivation,optical path design,algorithm development,simulation analysis and experimental verification are studied for the dual wavelength synchronous phase-shifting interferometry common-phase detection.The dual-wavelength synchronous phase-shift interference system was successfully designed and built,the segmented piston solution algorithm and the dual-wavelength fusion algorithm of principal component analysis were developed,and the detection software was constructed.The experimental verification proved that the system could meet the detection accuracy requirements of the theoretical analysis of the commonphase error,and realized the common-phase error detection based on the dualwavelength synchronous phase-shift interference method.It provides a common phase detection scheme for the future use of the segmented mirror system.