Acquisition and processing of three-dimensional information based on digital holography with pre-magnification

Abstract

According to the point-spread function of off-axis Fresnel digital holographic system with pre-magnification, the wave front deformation introduced by microscope objective is obtained. Using a collimated light as reconstructing wave, the phase aberration introduced by the difference between the reconstructing wave and the reference recording wave is analyzed by using a very simple method, which is very different from that one proposed by T. Colomb et al. Then the phase mask is obtained. It must be pointed out that for Fresnel digital holography, the recording distance must be determined accurately before compensating automatically the phase aberration. This is done by an automatic focusing procedure, which is based on image-gray-entropy-method. A special three-dimensional micro object is simulated, which is polluted by a random noise. The percentage error of the recording distance obtained by the focusing procedure is below 0.6 for SNR = 25. Then the accurate phase image is obtained by applying the automatic aberration compensation procedure. The simulation results show that for a hologram with high signal-noise-ratio, the above method is very effective; but for a very strong noisy hologram the procedure fails at all. Moreover, after applying a median filter to the primary reconstructed phase image, the aberration of the phase image obtained by further iteration decreases, at the same time the noise is strengthen. Therefore, the key of digital holography is the recording of high quality hologram.