The grating spectrometer has high polarization sensitivity due to the existence of grating and other dispersive elements, which will directly affect the quantitative data acquisition accuracy of the instrument. Therefore, it is necessary to establish the polarization factor calculation model and measurement method of the grating spectrometer, and then quantitatively describe the polarization effect of the instrument.. The analysis method of quantitative polarization error is founded in this paper, and the polarization measurement device of incident light at discrete wavelength is proposed, in order to achieve the monitor of quantitative polarization error of hyper-spectral detector at central-wavelength. Finally, the quantitative polarization error is analyzed in radiation calibration, and the in-flight polarization error is predicted based on the polarization of incident light measured by SCIMACHY.
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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