Research On Quantitative Phase Measurement With Digital Holographic Microscopy

Digital holographic microscopy is one of the most representative technologies in the field of quantitative phase measurement,and has been increasingly widely used in many fields,such as nanoparticle tracking,microfluidics,live cell investigation,characterization of micro-optics,MEMS measurement,life science,and so on,which benefits from its advantages of noncontact,label-free,high-resolution,low-cost,and fast reconstruction speed etc.It can obtain the intensity and phase of the object simultaneously with a single digital hologram.This dissertation focuses on the digital recording,numerical reconstruction and phase processing in the quantitative phase measurement with digital holographic microscopy.The goal is to explore an off-axis tilt compensation method and parabolic phase compensation with physical and numerical way,phase retrieval method based on the defocused holograms and the design of multi-mode digital holographic microscopy system.The major contributions in this dissertation are concluded as follow:(1)An off-axis tilt compensation method based on hologram rotation is proposed,which has been applied for the common-path digital holographic microscopy.In digital holographic microscopy with off-axis configuration,the tilt introduced by the off-axis angle,which is an important source of phase aberration in quantitative phase measurement with digital holographic microscopy.The rotated hologram can be obtained by rotating the original hologram with 180~°.Then the off-axis tilt could be removed by subtracting the unwrapped phase(-1 order)of rotated hologram from the unwrapped phase(+1 order)of original hologram,but without any complex spectrum centering selection,fitting procedures,or prior knowledge of the system.Some experimental results of microlens array and phase plate demonstrate the feasibility of the proposed method.(2)A physical method to compensate the parabolic phase aberration based on an electrically tunable lens is proposed.For the traditional digital holographic microscopy system,it always consists of a microscope objective in the object arm;this can improve the lateral resolution for the imaging of object.The parabolic phase aberration introduced by the use of microscope objective,which is another important source of phase aberration in quantitative phase measurement with digital holographic microscopy.To address this problem,an electrically tunable lens is inserted in the reference arm.By exactly controlling the external currents of the electrically tunable lens,we can obtain the different reference wave front to match the wave front introduced by different microscope objectives,but without complex alignment manipulations for optics element.The proposal is suitable for quantitative real-time phase imaging especially when it refers to multiple microscope objectives.The simulation analysis and experiment compensation results for different microscope objectives(4×and 10×)demonstrate the validity of proposed method.(3)A numerical method to compensate the parabolic phase aberration based on the the geometrical transformations of hologram is proposed.Numerical compensation method provides a new idea for compensating the parabolic phase aberration compared with the physical compensation method.After doing the geometrical transformations(vertical reflection,horizontal reflection,rotation with 180~°or transpose)for the original hologram,we can get a transformed hologram.By subtracting the unwrapped phase(+1 order)of transformed hologram from the unwrapped phase(+1 order)of original hologram,the parabolic phase aberration is compensated.The simple and effective performance makes the proposal available for single-shot quantitative phase imaging without complex numerical fitting procedures or prior knowledge of the specimen and system.The simulation analysis and experiment compensation results on micro-lenses array,phase plate,cell demonstrate the effectiveness of proposed method.(4)A phase retrieval method based on defocused holograms for digital holographic microscopy is proposed.The phase retrieval methods for digital holographic microscopy can be categorized into Fourier transform and phase-shifting technique.The Fourier transform method always need to obtain the full+1 orders with complex spectrum selection operation.The phase-shifting devices also need to be introduced for phase-shifting method.To address this problem,given three defocusing distances and three defocused holograms,the phase distributions of tested specimen can be reconstructed with a simple algebraic equation.We have deduced this equation in detail.To avoid the movement of system element or tested object,the defocused holograms can be flexibly and precisely obtained by introducing an electronically tunable lens based 4f system.The proposed method is suitable for an on-axis hologram as well as the off-axis one but avoids the requirements for not only the iterative process,complex spectrum selection in off-axis DHM or additional phase-shifting devices in on-axis DHM but also the assumption of tested specimen or previous knowledge of the system.The simulation analysis and experimental results of the microlens array and water drop demonstrate the feasibility of the proposed method.(5)A multi-mode digital holographic microscopy system is proposed.It not only integrates a transmission and reflection configuration with single wavelength but also a reflection configuration with double wavelength.The cube beam splitter has been used in proposed system to create the off-axis common-path geometry,in which both the object and reference beams pass through the same optical path.The common-path system not only keeps the system more stable but also removes the parabolic phase aberration.The transmission specimen and reflection specimen with single wavelength and reflection specimen with double wavelength have been measured and analysed with the proposed system.The experiment results demonstrate the practicability of proposed system.