Computer-aided alignment of off-axis three-mirror imaging spectrometer system

Abstract

The space camera is one of the most advanced optical equipments in obtaining earth surface information from space. With the development of the optical design, manufacture and alignment technology, the performance of the optical camera is moving forward quickly. In space-to-ground remote sensing field, the resolution of ground remote sensing images have become higher and higher. Off-axis three-mirror system becomes an advanced optical system structure of space camera at present, because of its merits of large field, long focal length, no obstruction, high modulated transfer function, wide spectrum, good image quality, small cubage and light weight, etc. As it is difficult to align and test, the alignment of off-axis three mirror system is time-consuming, so it is important and necessary of studying the computer-aided alignment of the complex optical system. Aiming at cutting the time of alignment, Computer-aided alignment technology is applied to this system. According to relation between fringe Zernike coefficient and Seidel aberration, wavefront aberration in the exit pupil of optical system is instead with fringe Zernike coefficient. A series of Zernike coefficient expressing the incorrect parameters of system are obtained by using multi-fields ZYGO interferometer auto-collimating interference test, which are transformed into geometric aberrations as the corrected object. Incorrect parameters of the system are determined by sensitivity matrix resulted from optical design software. These incorrect parameters are defined to be variables; the Zernike coefficient are defined to be the optimized target in merit function. The system is optimized by applying optical design software to receive the incorrect parameters result. Consequently, the adjusted result is brought into the optical design software to verify the right selection of incorrect parameters. The practical experiments are also given, result with RMS value lower than 0.04 lambda is acquired by using this alignment technology which has proved the effectiveness of above methodology of guiding-alignment.