Research on encode technology for aspherical surface measurement based on real-time hologram

Abstract

The aspherical measuring technology that based on computer-generated hologram (CGH) was introduced. The advantage of this method is that the phase shifts can be controlled digitally, no any mechanical moving and rotating element. By changing CGH coding which displayed on the Liquid Crystal Display (LCD), the wavefront and phase shifts in measuring system were induced. Based on the characteristics of aspherical measurement and LCD structure, the CGH encode technology used in LCD was discussed. Then a new encode method which applied to aspherical measurement was put forward. In this method, the LCD modulates functions of amplitude and phase was coexistent, and the character of LCD diffraction frequency spectrum was considered, and phase hologram was applied. This aspherical measuring technology is more flexible than usual method. In this paper, the hologram encode method based on LCD were illuminated in detail. In order to verify the correction of encode technology, the aspherical surface with standard wavefront was generated by coaxial hologram reconstruct system when hologram encode image was displayed on SONY LCX023 LCD, it interfere with the standard spherical wavefront, then the interferogram was sampled to computer by Charge Coupled Device (CCD) and A/D transfer, the wavefront of hologram reconstruct was obtained by image process finally. All calculation is completed by Matlab. An aspherical measuring system based on LCD was built experimentally. Both the theoretical analysis and experimental results demonstrate the feasibility of this approach.