| Digital holography derives from traditional laser holography. Photosensitiveelectron imaging devices are used to record the hologram instead of traditionalholographic recording materials, making exposure time greatly shortened. With thelarge-scale production of photosensitive electronic imaging devices and thedevelopment of digital image processing technology, digital holography showedvigorous vitality. Double exposure laser holographic detection technology can be wellapplied to detecting the defects in the subsurface of hierarchical structure. However,traditional laser holographic recording and representing process is cumbersome, sothe measuring efficiency is low. This paper, combined with the real-time advantage ofdigital holography, carried out the double exposure digital holographic detectiontechnology research.First of all, the basic theory of digital holography is studied including the recordingsetup, the conditions of recording, reconstruction method and the improvement of thereconstruction image. And in this paper, we choose off-axis Fresnel digitalholography as recording upset, and the Fresnel algorithm as the reconstruction.Then, the off-axis digital holographic recording conditions have been carried outand the optimum recording conditions are obtained. An integrated filter method isused to improve the quality of the reconstruction image.And then, double exposure off-axis digital holographic technology is used tomeasure tiny off-plane displacement of disc sample. The quantitative relationshipbetween double exposure interference fringes and the off-plane displacement areanalyzed, which verifies the feasibility of this technique on actual detecting.Finally, artificial sample of solid rocket motor coated grain and oil seal ring aredetected for defect respectively, which achieved detection accuracy up to2mm. |
