Gabor In-line Phase-shifting Digital Holography Using Phase-only Liquid Crystal Spatial Light Modulator

Gabor in-line digital holography has simple optical path, low influence from outside environment, and low requirements for the coherence of light source and spatial resolution of recording device, but zero-order image and conjugate image affect the quality of reconstructed image. Phase-only liquid crystal spatial light modulator can supply pure phase modulation on each pixel, so phase shift may be added into the spatial spectrum. According to the characteristics of phase-only liquid crystal spatial light modulator and Gabor in-line digital holography, we implemented Gabor in-line phase shifting digital holography based on4f system using phase-only liquid crystal spatial light modulator.The contents of this dissertation primary including the following:(1) The parameter relation of traditional Gabor in-line digital holography and Gabor in-line digital holography added4f system was deduced. On the basis of analyzing the parameters relation of traditional Gabor in-line digital holography, combining the parameters relation analysis of4f system, the parameter relation of Gabor in-line digital holography added4f system was deduced, laying foundation for the proposition of Gabor in-line phase-shifting digital holography based on4f system.(2) The principle and optical modulation characteristics of liquid crystal spatial light modulator are analyzed and discussed, the modulation characteristic curve measured.(3) Gabor in-line phase-shifting digital holography based on4f system was presented and providing the principle analysis and the corresponding experimental results. By analyzing the wave propagation, we introduced phase shift to zero-order spatial frequency of4f system, and gave a feasible method by using phase-only liquid crystal spatial light modulator to realize phase-shifting in the experiment. Moreover, we gave some experimental optical path, and carried out experimental verification. The study showed the feasibility and advantages of Gabor in-line phase-shifting digital holography based on4f system.(4) Automatic focusing of Gabor in-line phase-shifting digital holography based on4f system was analyzed, such as the selection of focusing criterion function and the advantage and accuracy. It showed that there were great advantages in automatic focusing of Gabor in-line phase-shifting digital holography based on4f system. It was the guarantee of the following three-dimensional shape measurement and surface measurement by Gabor in-line phase-shifting digital holography based on4f system.The above research proved the feasibility of Gabor in-line phase-shifting digital holography based on4f system and its unique advantages. It laid the foundation for the further study.