Reaserch Of High Resolytion Imaging Based On Spatio-temporal Scanning Digital Holography

Digital holography is a non-contact,high resolution imaging technology,which can obtain amplitude and phase information of an object simultaneously,and has the advantages of fast processing as well as numerical analysis on phase information.Because of the rapid development of computer and laser manufacturing technology,digital holographic imaging technology has been widely investigated.The phase information is related to the change of refractive index of an object or change of its internal structure.In particular,the phase information can accurately identify the structure distribution of transparent objects.Therefore,digital holographic technology has advantages over traditional optical imaging for transparent objects.Generally,because the tissue of plant cells is transparent,it is necessary in conventional optical imaging technology that cells have to be stained to observe them.Using digital holographic imaging technology can implement real-time imaging for living cells with no tags and no damage.In this thesis,the method of spatio-temporal scanning digital holography with improved resolution for imaging microfluidic is investigated.Research work is carried out on area-scanning recording of digital holograms and imaging reconstruction of spatio-temporal holograms to improve holographic imaging quality.The research mainly includes the following aspects.Digital holographic imaging for the measurement of microfluidic velocity in a microfluidic chip is carried out.The distribution of flow velocity in the microfluidic chip is characterized by the phase images reconstructed from the recorded digital holograms,which demonstrates the effect of microfluidic velocity on phase value.In the experiment,a Y-type microfluidic chip injected liquid is used for imaging,where the refractive index of the chip made of glass is different from that of the liquid.The reconstructed phase image in this digital holographic experiment shows the difference of refractive indexes between the chip and the microfluidic therein.The results of reconstructed phase show that the phase value increases with the increase of microfluidic velocity.The holographic recording scheme with area-scanning in spatio-temporal digital holography(STDH)is presented.The video holograms scanning along the X direction,Y direction and diagonal direction are recorded by spatio-temporal digital holography with area sensor CCD,respectively.The experimental results demonstrate that the image resolution is greatly improved by spatio-temporal scanning holographic imaging.By using different pixel columns of holograms,multiple spatio-temporal holograms each other with an extent of phase shift can be constituted directly from video digital holograms recorded only once,of which the procedure is illustrated in detail.After superposition processing of the amplitude images reconstructed from these phase-shift holograms,the image quality of the synthesis amplitude image is significantly improved.In the experiment,using a resolution test target as an object,the synthesis amplitude image of 64 amplitude images that are performed superposition processing for noise elimination shows significant improvement in image quality.The phase images of onion's living cells and their endoplasmic reticulum distribution are obtained by area-scanning recording and reconstruction imaging.By comparing the phase images reconstructed from the static-recording hologram and the area-scanning hologram,the results show that area-scanning spatio-temporal digital holographic method is quite effective in the improvement of image resolution and fidelity for imaging of living cells.Further,by using the above-presented superposition processing for multiple phase images,the cell nucleus and endoplasmic reticulum in cells are exhibited more clearly,and the clarity of phase images and the amount of endoplasmic reticulum that could be seen are obviously increased.The experimental results show that the area-scanning STDH method significantly increases the image resolution of onion's living celle,and the superposition processing of multiple reconstruction images each other with an extent of phase shift can effectively improve imaging quality of the reconstruction phase image.