Study On Lens-less Digital Holographic Microscopy

Digital Holographic Microscopy(DHM)is a new microscopic technique which combine digital holographic technology with optical microscopy. CCD is used to record information of hologram that the interference of enlarged object beam and reference beam instead of the traditional holographic dry plate, and then simulate the optical diffraction process of wave front for reconstruction of the original micro-object field, implementing a totally digitalized holographic process. DHM has the advantages of large field of view, high resolution, nondestructive, real-time 3D measurement, and has been becoming a hot research spot in optic science. It has been widely used in cell observation, biomedical diagnosis, micro-/nano device inspection, and so on.Through theory analysis, simulation computation and experiment demonstration, this paper addresses the basic issues of digital holography, including the light path of recording, the reconstruction algorithm, the factors of the imaging quality, the method of eliminating the influence of zero-order image and the twin image, and super-resolution image reconstruction. The main research content is as follows:(1) This thesis introduces the three main digital holographic reconstruction algorithms in detail: the Fresnel diffraction integral reconstruction algorithm, convolution reconstruction algorithm and the angular spectrum reconstruction algorithm, illustrate the applicability, advantages and disadvantages of each algorithm. Through analysis and comparison, we prove the angular spectrum reconstruction algorithm is the more accurate description of the optical diffraction process and it has strong applicability.(2) This thesis compares the on-axis digital holographic and off-axis digital holographic systematically, proves the on-axis digital holographic has more low recording requirements and in the CCD parameters is same case, on-axis digital holographic has high utilization rate of CCD space bandwidth, so it can record more object information and obtain higher resolution reconstruction images.(3) This thesis analyzes the influence of the imaging device CCD parameters on imaging quality: the pixel size of CCD main influencing the brightness of reconstruction image, the pixel pitch influencing the size of reconstruction image and the sensing area affects the reconstruction image resolution. We verify the analysis through computer simulation experiment and obtain the actual effects.(4) This thesis designs the optical path of lens-less digital holographic microscopy imaging, it use the LED light as the light source, to eliminate the influence of laser speckle noise and has many advantages such as low cost,small volume,light weight, easy to integration and so on. This paper verifies it’s feasibility through specific experiments and obtain the clear object reconstruction image.(5) In view of the zero-order image and the twin image’s influences on the reconstruction image quality, this paper introduces the HRO method that can eliminates zero-order and the iterative phase recovery algorithm that can remove conjugate like: GS algorithm and error reduction algorithm. We verify the validity of these algorithms in improving the quality of the reconstruction image through actual experiment.(6) This paper introduces the development process of super resolution image reconstruction and several reconstruction algorithms, improves the POCS algorithm that has most used in those algorithm. We prove the feasibility of super resolution imaging in increase the resolution of reconstruction image and improve the imaging quality through computer simulation and experimental validation.