Study Of Imaging Theory And Algorithm Of Digital Holographic Microscopy

Digital holography is a new three-dimensional imaging technique, whoseprinciples are similar to those of the traditional optical holography. It records digitalholograms by use of photosensitive electronic imaging device such as CCDs insteadof holographic plates, and simulates the optical diffraction process with a computenumerically. After the original wavefront is reproduced, the three-dimensional objectfield can be reconstructed and then quantitative measurement becomes feasible. Sothe whole holographic process of recording, storing and reconstructing is digitized. Inrecent years, digital holography has become a research focus in the field ofinterferometry, and has board application prospects in many aspects such asthree-dimensional topography measurement, vibration, deformation, particle sizeanalysis, cell culture observation, etc.In this thesis, the principles of digital holography, the algorithms of wavefrontreconstruction, and the two-dimensional phase unwrapping algorithms are studiedsystematically. And then an off-axis digital holographic microscope is designed anddeveloped. Finally, some samples are measured and the experimental results areinvestigated.The main contents of this thesis are as follows:1. The process of digital recording and numerical reconstruction of wavefront indigital holography are analyzed theoretically. And the principles of three-dimensionaltopography measurement, the recording conditions of holograms, the filtering methodto eliminate the zero-order and the conjugated first-order term are also studied.2. Three kinds of reconstruction algorithms for reproducing wavefront arestudied in detail. Their applicability, execution speed and reconstruction results areanalyzed and compared with each other, and these algorithms are proved to beconsistent.3. Two-dimensional phase unwrapping process to reconstruct three-dimensionalobject field is described in detail. Three sources of errors are pointed out, and then aneffective two-dimensional phase unwrapping algorithm based on sorting by reliabilityfollowing a noncontinuous path is described and illustrated with some simulatedexamples. Some improvements are put forward and the execution speed is improved evidently.4. Based on the Mach-Zehnder interferometer, an off-axis digital holographicmicroscope with pre-magnification is designed, and the corresponding software isalso programmed. Some samples are measured on this experimental system, and thenthe intensity maps and three-dimensional phase maps are reproduced at the same time.Finally, the experimental results are investigated.