Experimental Study On A Practical System Used For Recording And Reconstructing Digital Holograms

Nowadays, the resolving power of the reconstructed image in the applications of digital holography is restricted by the finite size and resolution of the CCD. And the phase unwrapping, as an important process, hasn't been perfectly solved in digital holographic interferometry. In this dissertation, we discussed these two problems, which restrict the applications of digital holography, and presented some improved methods. Basing on these, we developed a practical experimental system for effectively recording and reconstructing digital holograms. The main contents are as follows:(1) Some methods for recording and reconstructing digital holograms with large size are proposed. Based on breadthwise moving the CCD camera precisely, a hologram with large size can be obtained by image fusion. For the processing limitation of the computer and the influences of the critical angle between the object and reference beams, a method is proposed based on theoretical analyses, which is demonstrated to be feasible for segmenting, reconstructing, and fusing digital holograms by the experimental results.(2) After the frequency aliasing in reconstructions of under-sampled digital holograms are investigated both theoretically and experimentally, a novel method based on the sub-pixel imaging technique is proposed to reconstruct digital holograms with large size and high resolution. The experimental results show that the method can overcome the limitations of the critical angle between the object and reference beams, and omit the frequency aliasing.(3) A model to effectively eliminate local branch points without influencing normal points is established. And then, by calculating the mean values of the unwrapped phase along multiple certain directions, the goal of path independence can be achieved. Employing numerical simulations and experiments demonstrate the feasibilities and the efficiencies of the approach. It is shown that the proposed method also exhibits very strong stability and high efficiency even in presence of serious noises and relatively large under sampled areas.(4) By mixed programming between MATLAB and VC++, a practical system for recording and reconstructing digital holograms is developed by packaging the current and previous work in our laboratory. Recording, reconstructing, and pre-processing can be easily implemented by the system, which has good man-machine interface, high computational speed and better stability.