Study On Polarization Grating Based Point Diffraction Digital Holographic Microscopy

As a quantitative phase imaging technology,digital holographic microscopy(DHM),which combines digital holography with optical microscopy,can quantitatively obtain the threedimensional morphology and refractive index distribution of cells and other samples from the intensity and phase images reconstructed from holograms.It is an effective full-field quantitative,non-contact,fast,and high-resolution three-dimensional imaging technology.In recent years,with the development of electronic imaging devices and computer technology,DHM has been widely used in the field of living biological cell detection and has made significant progress.To improve the non-adjustable contrast of interference fringes in traditional diffraction phase microscopy,a point diffraction digital holographic microscopic imaging system with adjustable contrast based on polarization grating was designed and built in this paper.Then the mature lily anthers and living paramecium were studied.The main research contents and achievements are as follows:1.The basic theories of digital holography are analyzed and studiedDigital holography includes two basic processes: wavefront recording and wavefront reconstruction.The former changes the amplitude and phase modulation of the original object wave into the intensity modulation of the hologram to realize the recording of the hologram,and the latter performs the opposite process to realize the wavefront reconstruction of the object wave.In this paper,the optical path of spherical reference wave digital holography is analyzed,and several specific optical paths are discussed,and the corresponding recording conditions are given.In addition,several common phase reconstruction methods are studied and analyzed.Among them,the first three methods are all based on scalar diffraction theory and implemented by FFT.In terms of reconstruction speed,Fresnel transform method is the fastest,and the convolution method is the slowest.The wavelet transform method,which overcomes the shortcomings of discrete Fourier transform and improves the calculation speed and image quality,is based on wavelet theory.2.The diffraction theories of polarization grating and the design scheme of this paper are analyzed and verifiedFirstly,the diffraction theory and diffraction efficiency of liquid crystal polarization grating are analyzed and discussed by Jones matrix.Then,a series of verification experiments on the diffraction characteristics of the selected polarization grating are carried out on the preliminary experimental system.The results show that the intensity of two waves presents the opposite change trend when rotating the quarter-wave plate.Combined with the excellent diffraction characteristics of the polarization grating,the intensities of the object wave and the reference wave are well modulated.It is proved that it is feasible to adjust the fringe contrast by rotating the quarter-wave plate,which lays the foundation for the design and construction of the experimental system.3.Based on DHM,a point diffraction digital holographic microscopic imaging system is designed and builtA digital holographic microscopic imaging system with adjustable interference fringe contrast based on polarization grating is designed and built.Combining the schematic diagram and physical diagram of the system,the imaging process and main devices are well presented.Then,the Jones matrix is used to analyze the imaging principle of the system,and the imaging field of view,actual magnification,resolution,etc.,are analyzed.To promote the imaging capability,the imaging system is optimized and miniaturized.Finally,we analyzed the advantages of the system.It shows that the system not only has the advantage of high phase measurement accuracy of traditional diffraction phase microscope,but also has the advantages of real-time imaging,high stability and high sensitivity.It is very suitable for quantitative measurement and dynamic observation of phase biological samples such as living cells and tissues.4.Based on the point diffraction DHM imaging system,several experiments are conducted Based on the built DHM imaging system,several experiments are conducted to verify the system performance,and then the mature lily anthers and living paramecium are imaged and studied.The experimental results show that the intensity of the reference wave and the contrast of interference fringes are related to the specific sample,so it is very important and meaningful to realize the adjustable contrast of interference fringes.At the same time,compared with the traditional separation system,the system has a long-time stability.In addition,the system can adjust the contrast of interference fringes by rotating 1/4 wave plate combined with the diffraction characteristics of polarization grating,and the system has high sensitivity.The system was used to image mature lily anthers and other samples,and the results show that the phase image can display more details of the sample than the amplitude image.Finally,the imaging experiments of living paramecium based on this system are introduced.The spiral movement process of living paramecium in the mixed solution of glue and water and the circular transportation process of food bubbles in the body are successfully captured.The spiral movement law and morphological parameters of paramecium are preliminarily explored.