The Study Of The Technique For Particle Field Measuring With Digital Holography

As the name suggests, the Digital Holography is the combining of the moderndigital technology and the traditional optical holography technology. It uses aphotodetector to record the hologram, and reconstructs the hologram in the computer.In a wide range of fields, the particle field measurement has an extremely importantsignificance. Currently, more and more people use the means of Digital Holographyfor particle field measurement, and a huge advantage has been showed. The opticalsystem is very simple, and the three-dimensional distribution, size, and flow rate ofthe particle can be quickly measured. This paper focuses on Digital Holography forparticle field measurement. The mainly work will be introduced later.First the research status quo of Digital Holography at home and abroad hasbeen introduced, and some applications with Digital Holography has been list.The basic principles of the digital have been studied, and the mathematicalmodel of the Digital Holography for particle field measurement has been showed. Inthe particle field holography, the coaxial holographic optical record is always used,as it is simple, and due to the small particles, the impact of the conjugate image canbe ignored. Finally, the different of spherical wave and plane wave for recording arecompared, and the shortcoming of the spherical wave for recording has been pointedout.Three commonly used algorithms for reconstruction, named SFFT-FR,FFT-CVFR, FFT-AS, has been studied. Then, the scope of application of thesealgorithms has been deduced. We thus conclude that the SFFT-FR is not accord withthe sampling theorem, the FFT-CVFR is applicable when the distance ofreconstruction is greater than the distance of boundary, and the FFT-AS is applicableanywhere.Study several auto-focus algorithms, and then introduce an auto-focusalgorithm which is based on the frequency spectrum. Using experiments show thatthis anto-focus algorithm can accurately calculate the location of the particle, andthe efficiency is much larger than the commonly used algorithm which is based onthe gray value gradient.Record the hologram of the plankton, and then measure this particle field usingdigital holography technology. As a result, we reconstruct the particle field and theclear image of the plankon. At last, we use the resolution board to analyse theresolution of this system, and we find that we can distinguish a stripe which has a8μm spacing with this system.