Alignment technology based on a central small aperture for the AIMS telescope.

The accurate infrared solar magnetic field measurement system (AIMS) is a 1 m off-axis Gregorian alt-azimuth solar telescope and will be dedicated to measuring the solar magnetic field in mid-infrared. How to align the large-aperture off-axis system is a significant issue. Sub-aperture stitching with the small-aperture standard flat mirror can be applied to the alignment of the large-aperture off-axis system. However, this method is time-consuming and inefficient. We propose an alignment method based on the Zernike polynomials of the central small aperture to solve the low efficiency of sub-aperture stitching. Theoretical simulation shows that the RMS residual error of the system after using the central small-aperture alignment method will be less than 4.5∗10-6λ at 632.8 nm. Practical alignment suggests that our method can make the RMS value of full-aperture wave aberration quickly converge to 0.12λ at 632.8 nm. Compared with the sub-aperture stitching method, our method can significantly reduce the times of sub-aperture stitching and save the alignment time.

Wavefront reconstruction algorithm based on Legendre polynomials for radial shearing interferometry over a square area and error analysis.

Based on the Legendre polynomials expressions and its properties, this article proposes a new approach to reconstruct the distorted wavefront under test of a laser beam over square area from the phase difference data obtained by a RSI system. And the result of simulation and experimental results verifies the reliability of the method proposed in this paper. The formula of the error propagation coefficients is deduced when the phase difference data of overlapping area contain noise randomly. The matrix T which can be used to evaluate the impact of high-orders Legendre polynomial terms on the outcomes of the low-order terms due to mode aliasing is proposed, and the magnitude of impact can be estimated by calculating the F norm of the T. In addition, the relationship between ratio shear, sampling points, terms of polynomials and noise propagation coefficients, and the relationship between ratio shear, sampling points and norms of the T matrix are both analyzed, respectively. Those research results can provide an optimization design way for radial shearing interferometry system with the theoretical reference and instruction.