Some Issues In Recording And Reconstruction Of Near Distance Digital Holography

Digital holography was first proposed by Goodman in 1967, by use of photosensitive electronics imaging apparatus to replace the traditional hologram recording material to record hologram, and kept the hologram in computer, then use computer simulate reconstruction light to replace optics reconstruction light, implemented recording and reconstruction of the first digital hologram. Because of the limit condition of computer and recording apparatus, digital holography developed very slowly, as far as the end of 1990s digital holography stepped into a period with rapid progress. At the present time digital holography is widely used in shape measurement, distortion shaking measurement, micro observation, information encryption, particle measurement, digital watermarking et al.A key problem of digital holography is how to improve the resolution of reconstruction image, premagnification digital holography and aperture synthesis digital holography are two widely used method to improve the resolution of digital holography, according to analyze the basic theory of digital holography and the experiment research, shorten the recording distance is a direct method that can improve the resolution of digital holography, but when recording distance is nearer than the Fresnel condition the fast Fourier transform can be not used in reconstruction compute, the problem brings big trouble. In this paper, this problem is the main focus, according to analyze and experiment, the problem was solved and the resolution achieve 10 μm. In this paper, the main innovative ideas are as following:(1) ,On the base of introduction the recording and reconstruction of digital holography,aim at the high order phase which can not be omitted, in this case fast Fourier transform can not be used in reconstruction compute. A phase compensation method is proposed in the paper which makes the high order phase of reference light to counteract the high order phase of object light and the whole reconstruction compute fit the condition of fast Fourier transform.(2) ,According to the ratio of Z_rh/Z_oh discuss the fit condition of phase compensationmethod, result shows, in the condition of near recording distance, the distance form the reference light to CCD is strictly limited, along with the augment of recordingdistance, the limit to the reference light is less strict, in actually operation we only choose the suitable ratio of Z_rh/Z_oh, the high order phase can be compensate small enough.(3) ,The actually used reference light is not ideal spherical wave in near recordingcondition, it may have aberrance in both x and y direction, the reconstruction light is simulated by computer and it is ideal spherical wave, the difference between the actual reference light and the simulate reference light make the reconstruction image very serious aberrance. Aim at this problem we emendate the reference light according to import a appending phase and acquire the high quality reconstruction image.(4) , Validating the above analysis according to experiment.