Optimization Of Digital Holography For Real-time Microscpic Imaging Of Living Cells

The research of biological samples is the important topic in the field of life science research.Researchers can observe the living biological cells by means of microscopic imaging.Quantitative imaging for living cells is of great significance,because the dynamic process of cells partly reflects the progress of life circle.Cells that have the characteristics of light transmission,complex structure,small volume,can be imaged by imaging technology that sensitive to the refractive index and thickness of cells.Digital holographic microscopy imaging has great advantages in quantitative imaging for this kind of phase objects.The advantages of digital holography microscopic imaging technology in high sensitivity,high resolution,fast and nondestructive measurement make it especially good at real-time observation of cell internal tissue and its life process without damaging cells.Three-dimensional microstructure and dynamic cells can be imaged in real-time by digital holographic imaging technology,the contour and refractive index of objects also can be quantity analyzed with the development of digital holography.In recent years,the application of digital holographic imaging technology in life science,material science and other fields has been further studied.In this thesis,the digital holographic imaging with sptiao-temporal scanning based on area array CCD and the real-time imaging with dual-wavelength digital holographic microscopy are optimized.The main contents are as follows:In the first part,the recording process of spatio-temporal scanning holography is improved,the quality of reconstructed image can be enhanced by construction of the spatio-temporal hologram in accordance with the four-step phase shift or constructing an on-axis space-time hologram to have a further optimization.Firstly,the spatiotemporal scanning digital holographic optical system is built based on Mach-Zehnder interferometer structure,and a sequence of holograms of a target object is recorded in real-time by scanning the object's area to be imaged.Then,the spatio-temporal hologram can be synthetizing by combing the chronological extracted single column hologram traversed by the baseline that a pixel column in the recorded hologram sequence is set as.In addition,the spatio-temporal scanning holography can achieve a high quality reconstruction image,when the zero-order spectrum item is eliminated by four-step phase shifting method.The elimination of the zero-order spectrum item can be realized by synthetizing four spatio-temporal holograms from different base line in the process of reconstruction.The spatio-temporal holograms that satisfied four-step phase shift method can be easily obtained by using the real-time quantitative adjustment of system,which combining the frequency domain method that can calculate the phase value from coordinates of frequency domain and MATLAB in the construction of spatio-temporal scanning system.Secondly,an on-axis spatio-temporal hologram can be synthesized by adjusting the interference fringe angle of the off-axis interferogram to make it orthogonal to the scanning direction in the experiment of spatio-temporal scanning imaging.The experiments show that the construction of on-axis spatiotemporal spatio-temporal hologram is simple,in which the zero and negative order of frequency spectrum can be easy eliminate in the process of reconstruction by using four-step phase-shift method.Moreover,there is no need to eliminate the phase distortion caused by off-axis optical structure in situation of using the same phase shift method.In the experiment of the dragonfly wings and other samples,the imaging results show that the optimization of spatio-temporal scanning digital holographic imaging can improve the quality of reconstructed phase and amplitude images.In the second part,we improve the experimental system of dual wavelength digital holography,and analyze the noise characteristics of phase reconstruction in dualwavelength digital holography.Firstly,a real-time dual-wavelength digital holographic imaging system based on polarization multiplexing is proposed,which can perform single exposure recording of dual-wavelength digital hologram and flexibly adjust the spectrum position to reduce the influence of the zero-order spectrum.In the experiment,the ability of single exposure recording is verified via reconstruction of the amplitude and phase images of the microfluidic channel from a single dual-wavelength hologram.Secondly,the expansion of axial measurement range of dual-wavelength digital holographic system by using linear regression phase recovery method is verified by simulation.In addition,the amplification and suppression of phase noise in dualwavelength reconstruction are discussed in simulation and experiment.