Research On In-line Incoherent Phase-shift Digital Holographic Microscopy Imaging Characteristics

Digital holography,born in the 1960 s,can be applied to vibration measurement,three-dimensional shape measurement,phase detection and other fields,because it can simultaneously obtain the phase and amplitude information of samples.However,the requirement of high coherence of light source makes its application and extension be limited.In recent years,with the practical and commercial high-speed Spatial Light Modulator(SLM)being promoted,SLM-based incoherent digital holography has been highly concerned by researchers.It can record the three-dimensional spatial information of objects under the illumination of the incoherent light without any scanning equipment and moving parts,which overcomes the shortcomings of the laser digital holography whose system stability must be high.While its structure is simple,its reconstruction is flexible,and it can match any optical system,so its academic research value and practical application value is very high.Based on analyzing the principle of the in-line incoherent phase-shift digital holography,the point spread function,the lateral magnification and the reconstruction distance factors are given.The factors influencing the imaging resolution of the system are discussed.Its simulation is carried out by MATLAB,and the three-dimensional imaging characteristics are verified.By optimizing the system structure parameters,a high quality reconstruction image is obtained.On this basis,the reflective and transmissive holographic microscopy imaging system are proposed to verify the three-dimensional micro-imaging characteristics.The effect of SLM pixel multiplexing on the image quality is discussed.Finally,the helical phase modulation is achieved by SLM,and the simulation is carried out on the computer to verify the characteristics of image edge enhancement.The influence of the topological value on the image quality is also analyzed.The paper mainly includes the following four aspects:(1)Based on the analysis of traditional optical holography recording and reconstruction,the basic principle of digital holography is discussed.The common hologram reconstruction algorithms are introduced and compared,and the angle spectrum algorithm is analyzed emphatically.The advantages and application of digital holography are summarized.In-line hologram is compared with off-axis hologram.The phase-shift technique in in-line holography is described detailedly.(2)Based on the incoherent holography theory,the point spread function(PSF)of the SLM-based in-line incoherent phase-shift digital holography recording optical path is deduced from wave optics,and the mathematical expressions of the lateral magnification and the reconstruction distance are obtained.Influencing factors of resolution are analyzed.The three-dimensional imaging characteristics of "S","L" and "M" are verified by computer.Experiment on the USAF Resolution Target with the recording optical path is accomplished,and high-quality reconstruction images is obtained.(3)The SLM-based incoherent digital holographic microscopy system is built.Experiment on the USAF Resolution Target is accomplished,and the same resolution as that of the traditional wide-field microscope is obtained.The imaging of the plant cells was carried out by the transmission holographic microscopic optical path,and the experiment on the pinhole of 20?m was carried out to give the further explanations on the effect of the image quality when the pixels on SLM are multiplexed.Experiment on a diamond with the size of 300?m 500?m is finished by the reflective microoptical path,and the best reconstruction images on different focal planes are gotten,which verify the three-dimensional microscopic imaging characteristics of it.(4)The helical phase modulation is maked by SLM,and the simulation is carried out on the computer to verify the image edge enhancement characteristics.By experimenting on the pinhole with the size of 20 ?m,the reconstruction images under the double lens phase mask and the helical phase mask are compared.And the effects of different topological charges on the reconstruction images are analyzed.