The Elimination Of The Twin Image And The Auto-focusing In Gabor In-line Digital Holography

Gabor in-line digital holography has simple recording optical path, low requirements of the coherence of light source, low resolution ratio of recording device, and little influence by environmental vibration and air turbulence. Because of these advantages, it is widely used in the area of particle field detection, optical interferometry, biomedical microscopic imaging and testing, and so on. The key problem of the Gabor in-line digital holography to be solved is automatic focusing and eliminating the influence of zero-order image and the twin image. This paper finds that the method is very sensitive to the distance deviation in the study on the eliminating the zero-order image and the twin image using the multi-plane reconstructed algorithm. Based on this phenomenon, combining the multi-plane reconstructed algorithm with the appropriate focus function, this paper proposes an automatic focusing based on Gabor in-line digital holography multi-plane reconstruction.The main research content is as follows:(1) Through the comparison the parameter of off-axis holographic recording optical path, this paper proved:1) Gabor in-line digital holography has the low requirement of the CCD resolution ratio.2) Gabor in-line digital holography can record large size range of the object.3) The utilization rate of the CCD spatial bandwidth is high.4) The lateral resolution of the reconstructed image is high.(2) This paper makes a detail introduction of several major methods about eliminating the zero-order image and the twin image using in Gabor in-line digital holography (including the average reduction algorithm, the HRO subtraction algorithm, the phase retrieval algorithm, the segmented filtering algorithm, the multi-plane reconstructed algorithm and two holograms algorithm). Through theoretical analysis, experimental simulation and optical experimental verification, the paper describes the characteristics, advantages and disadvantages, as well as applicability of each algorithm in detail. (3) The paper deduces that Gabor in-line digital holography multi-plane reconstructed algorithm is sensitive to the distance deviation. Based on it, the paper combines the algorithm with the appropriate focusing function, which improves the precision and sensitivity of Gabor in-line digital holography automatic focus. The above conclusions are simulated by experimental simulation and optical experimental verification.The above study provides a convenience on the choice of the method in el iminating zero-order image and the twin image, and makes the automatic focusin g more accurately. It has laid a good foundation for solving the multi-particle d iscrimination issues under the different levels, as well as the granular segmentati on and independent focus problems.