This paper proposes an interferometry method based on a fixed interferometer structure and locally compensated stitching. The subaperture measurement is completed by applying a double-optical-wedge compensator in the "rugged" area of the surface that cannot be measured. The data of the measured area is stitched to obtain the local surface shape. The calibration of the double-optical-wedge compensator is performed by using a standard mirror. Surface figure error (SFE) of the standard mirror is measured by an interferometer beforehand. Compared with the SFE measured after adding the compensator in the optical path, the phase and aberration of the double-optical-wedge can be obtained. Measured data is processed by the subaperture stitching algorithm. Through the weighted fusion algorithm, the corresponding data values on the overlapping areas are weighted, and different weights are assigned to different areas to make the stitching transition smooth. Based on the principle of interferometry, a double-optical-wedge compensation measurement system is designed and implemented. A simulation model of the measurement experiment is presented, and the validity of the method is verified by simulation.
Computer-generated hologram (CGH) method is a high-precision aspherical surface detection method. CGH produces wavefronts of any shape with extremely high precision and is adopted in null test. Liquid crystal CGH (LC-CGH) is a new type of CGH with short production cycle and low cost. It is a promising alternative to traditional CGH. In this paper, the overall process flow of LC grating preparation is presented. The influences of three process parameters, such as LC solution concentration, spin coating speed and time on the three physical quantities of LC grating diffraction efficiency, LC polymer film thickness and phase delay are studied. Based on the analysis, improvement measures are proposed for the preparation process. The research carried out in this paper has guiding significance for the processing and manufacturing of LC-CGH.
We propose a liquid crystal (LC) hologram fabricated with photoalignment technology, for the measurement of a cylindrical surface. A standard cylindrical surface reflects the incident planar wavefront and generates an interferogram with a planar reference wavefront. Photoalignment azo-dye material is then exposed by the interferogram and aligned with desired orientations, following with depositing LC monomer to generate the designed phase information. After ultra-violet curing, the fabricated LC hologram plate can generate a standard cylindrical wavefront when illuminated with a planar wavefront. The minimal line-width due to the limitation of LC molecules is sub-microns, which is smaller than the limitation in traditional CGH. The systematic design of the measurement is proposed, followed by a demonstration simulation.