The Research On Programmable Point Source Digital In-Line Holographic Microscopy Based On DMD

Digital holographic technology is combined with microscopy to accurately analyze the amplitude distribution and phase information of an object and obtain three-dimensional information,which cannot be replaced by other microscope techniques.The digital in-line holographic microscope system has a high utilization of space-bandwidth product of the detector,so it has got tremendous attention and research for its good performance.The commonly used pre-magnified imaging system requires the microscope objective lens to obtain the amplified object wave,which increases the aberration of the system and also limits the field of view.Another imaging system is based on the Gabor point-source digital in-line holographic microscopy,which has a simple structure and does not require the microscope objective.Taking advantage of the diffraction effect that spherical wave has to achieve the amplification of object wave is a research hotspot in recent years.In order to overcome the shortcoming of the limited field of view in digital holographic microscope system,this thesis aims to find a point source scanning method that does not need the mechanical device.And this method is applied to the Gabor point source digital in-line holographic microscope system to achieve the theoretical and experimental study about the expansion of the field of view.Due to the interference of conjugated images existing in the Gabor point-source digital in-line holographic microscope system,this thesis improves the phase recovery iterative algorithm,and carries out theoretical simulation and experimental verification.According to the characteristics of digital micromirror device DMD which can be controlled by single pixel and be encoded independently,the micromirror of DMD is equivalent to the point source of the system.Through the control of software,a programmable point source scanning method is implemented.The main contents are as follows:1.Optimize the constraints of the phase recovery algorithm.Based on the existing phase recovery algorithm,we have added constraints of the phase of the point source on the object plane so that it can be better applied to point source digital in-line holographic system to remove conjugated image.We choose resolution plate and object with high-transparency as samples in simulation and experimental verification,and the results of iteration prove that the improved algorithm is more suitable for object with high-transparency.2.DMD is actually a complex two-dimensional blazed grating.The understanding of its diffraction characteristic is the key to realizing the programmable point source scanning method.Based on the physical diffraction model,this thesis simulates and experimentally verifies the influence of the incident angle on the characteristics of DMD.Finally,(24~o~ 43.8~o)is selected as the optimal range of incident angle of the system.This angle enables us to set up the system properly and fully utilize the DMD's diffracted energy.3.The programmable point source scanning method is applied to the Gabor point source digital in-line holographic microscope system.A mathematical model of programmable point source scanning is established.And the basic principle,implementation process and test results of the system are described in detail.It is proved that the final detection field of view has been expanded to 2.05 times as compared with the initial field of view,indicating the feasibility of this method.The experimental system with simple setup also avoids mechanical scanning of the detector or object.