Design Of Micro Particles Imaging System Based On Lens-free Digital Holography

With the development of the shipping industry in our country,the problem of cross regional transmission of microorganisms in the ballast water is more and more serious.The traditional imaging and detection equipment has many disadvantages,such as large volume,high cost,high level of operation,and can not be detected on the spot.In order to realize the imaging and detection of microalgae in ballast water.In this paper,a kind of in-line lens-less digital holography micro particles imaging system was designed.The system realized the imaging of the micro particles and obtained the three-dimensional morphology and the three-dimensional size of the particles.The imaging of platymonas in the ocean showed that it can be used for the imaging and activity detection of the marine microalgae.The mainly completed works are as follows:(1)Based on the scalar diffraction theory,the parameters such as the wavelength of the light source,the aperture of the pinhole,the distance between the light source and the sample,and the sample's recording distance of the in-line lens-free holographic micro particles imaging system were analyzed.And the relationship between the parameters was deduced.The best parameters of the in-line lens-free holographic micro particles imaging system can be obtained in accordance with the relationship when designing the imaging system.(2)A in-line lens-free digital holographic micro particles imaging system was designed.The system used a partially coherent light source LED as the light source of the holographic interference.And the light source increased it's coherence by coupling a small pinhole.The hologram was obtained by the CMOS imaging sensor,whose lens was removed,with the cover glass as it's platform.(3)Comparing and analyzing the Fresnel integral transform reconstruction method,the Fresnel convolution method and the angular spectrum reconstruction method.The application range of different reconstruction method was obtained.The formula of the reconstruction distance was deduced when using the angular spectrum reconstruction method.(4)By using the twin-image elimination method,the twin-image of the in-line digital hologram was eliminated and the virtual image was reconstructed.And the true phase of the micro particles was obtained by using the unwrapped method.Then the three-dimensional morphology was reconstructed,and the three-dimensions dimensions were obtained.(5)The hologram of platymonas was captured and reconstructed,the twin-image of the reconstructed image was eliminated,and the three-dimensional morphology was reconstructed.The phase information and the microscope image of the platymonas were compared,the activity of the platymonas was determined.The results show that the system could not only obtain the information of microalgae,but also be used for the activity detection of microalgae in the ocean.