Experimental Study Of Digital Holographic Microscopic Imaging

Conventional optical microscope is characterized by a small depth of focus due to its high objective's numerical aperture and magnification ratio. It can not record and reconstruct the 3-D information of object. For the analysis of a three-dimensional sample it then requires a mechanical motion along the optical axis to scan the complete experimental volume. By using of holography, the object wave-front, including amplitude and phase, can be simultaneously recorded though interfering with a coherent reference wave, and then can be reconstructed optically. With the recent developments of digital holography, where the hologram information is directly recorded on a CCD camera, the optical reconstruction is replaced by a computer reconstruction.In digital holography, the hologram is directly recorded on a charge-coupled device(CCD) camera and its reconstruction is carried out by computer numerical calculation instead of optical diffraction used in conventional optical holography, so its whole process including recording, storage and reconstruction is digitally realized. Digital holography has been attracting intensive research efforts during recent years due to its potentials in automated high-resolution deformation measurement and shape analysis, microscopic imaging and testing, particle size analysis, as well as encryption of information and display, etc. In this paper, the principle of digital holographic microscopy is analyzed, the basic experimental system is designed, and some elementary experimental results are obtained.Firstly, some methods of digital holography were analyzed, including four-step phase shifting method and Fourier spectrum filtering methods. Secondly, the experimental set-up is designed and its fundamental parameter relationships are analyzed, including recording sampling requirement, reconstructing separation condition, and resolution. Finally, its application in microscopy is studied, some results are obtained, some reasonable explain for the experimental results are given.