This study designed a large aperture infrared diffraction system that utilizes Schupmann's achromatic theory to achieve wavelength tunable high-resolution imaging. The impact of stitching error on imaging quality was analyzed based on geometric optics, and simulation analysis was conducted on stitching error based on wavefront aberration. The results indicate that the system has reached the diffraction limit of imaging quality in the design band, and both wavefront aberration and distortion are within acceptable ranges. Splicing error analysis shows that translation error has a significant impact on imaging quality, while edge mismatch error and tilt error have a smaller impact. This system has the characteristics of lightweight and low cost, and is suitable for various space observation tasks.
The urgent need for the precise, real-time position metrology between the optical components in a modern space camera is becoming more critical with the increased resolution, aperture, focal length, and light-weighted structure. Gravity offload, composite material humidity desorption, temperature cyclical variation with the illumination, and micro-vibration on platform would introduce unpredictable affect to decrease the imaging quality. The solution of the optical system disorders would mainly rely on the ground-based stimulation and on that basis, active optics compensation, which could not be accurate. This influence expands within the opto-mechanical structure complexity. This paper represents an implement solution for position and attitude metrology used for on-orbit real-time measurement. To deal with the contradiction of system accuracy and simplicity, we simplified the system to a measurement model equivalent to 6 degree of freedom Stewart Platform structure. The works on this paper tightly coupled to the accuracy requirement of a long focal length optical system. After carefully compare the systematic requirement and balance the implementation costs, we applied the common-path, multi-channel heterodyne interferometers to accomplish the large-scaled coarse measurement for the step disturbance and small-range fine measurement to sense the ambient vibration. The metrology accuracy analysis and error evaluation indicated an effectiveness of this metrology system, which met the requirement of our given optical system. It was indicated in this paper that the metrology method could be generalized in other optical systems and similar long focal length optical systems in the future.
KEYWORDS: Diffraction, Segmented mirrors, Telescopes, James Webb Space Telescope, Error analysis, Optics manufacturing, Sensors, Signal detection, Visibility, Signal processing
Two-Dimensional Dispersion Fringe Sensing (TDDFS) is an efficient method for coarse phasing of segmented mirrors. Modeling and simulations based on double-aperture diffraction are used to study dispersion fringe in two directions. In the dispersion direction, the nonlinear least squares fitting method is used to extract the piston error. The theoretical capture range is ±96μm which is verified compared with the simulation results, and the detection accuracy can be reached to λ/10. However, the nonlinear least squares fitting method cannot effectively detect piston errors within one wavelength. In the diffraction direction, the principal maximum extraction method is used to measure the piston error, which is suitable for the piston error detection with a small range within one wavelength. In order to reduce the influence of the extraction error of the center line, we propose a corrective method. The results show that the accuracy of the modified principal maximum extraction method can reach 30nm. The two methods can effectively meet the requirements of the piston detection of the large-aperture segmented mirror telescopes.
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