ABSTRACT
At present, aluminum-based optical payloads are widely used in the aviation and aerospace field, and the demand for aluminum mirrors has become increasingly urgent in the visible light region. The main processing of an aluminum alloy mirror involves single-point diamond turning followed by a combined polishing process. Among these processes, magnetorheological finishing (MRF) is an important method for improving a surface figure. During the MRF process, excessive impurity contaminants are introduced into the surface of the aluminum mirror, thereby reducing surface reflectivity. In this paper, theoretical analysis and time-of-flight secondary ion mass spectrometry depth profiling were used to obtain the cause of pollution, and the process scheme of femtosecond laser cleaning was proposed. After verifying the feasibility, a new, to the best of our knowledge, process route was implemented on a Φ50mm aluminum mirror. Finally, the surface figure of RMS 0.022λ and the surface roughness of Ra 3.24 nm were obtained. In addition, reflectance in the visible light and near-infrared bands has increased by about 50%.
ABSTRACT
A computer-generated hologram (CGH) is the core component for an aspheric surface test. According to fabrication demands, it is necessary to convert the designed CGH phase compensation function into the processed pattern, that is, the fringe discretization process. In this paper, we propose a new discretization method for a CGH in a test of the freeform surface, and realized the encoding of processed fringes by MATLAB software. Furthermore, we designed the experiment to verify the accuracy of the new discretization method and compared the calculation efficiency between the new algorithm and the reported algorithm. Finally, based on the testing requirement of a freeform mirror in a camera optical system, we completed the design, encoding, and fabrication of the CGH sample, and analyzed the influence of various errors on wavefront accuracy of the CGH.
