A Study On The System That Uses Off-axis Digital Holography To Detect Particle

Holographic technology has broad application prospects in digital holographic microscopy,three-dimensional shape measurement,image recognition,image anti-counterfeiting and encryption,medical diagnosis,and three-dimensional tomography.In this paper,a particle detection system has been designed based in holographic theory.The system uses an off-axis configuration which is based on Sagnac interferometer.The biggest feature of the Sagnac interferometer is that the two beams of laser are on the one way,which improves the stability of the progress of recording of hologram,making it possible to develop a small embedded digital holographic system.Compared with the traditional off-axis holographic instruments,the object to be tested is placed outside the interferometer module,which is more advantageous for the miniaturization and integration of this instrument.Starting from the basic theory of digital holography and taking the recording and reproduction of hologram as the core,the research work mainly focuses on the hardware design and software design of the off-axis digital holographic particle detection system.The main research contents and results are as follows:1.Combining the shortcomings of current in-line and off-axis holographic instruments,the advantages of using Sagnac interferometers in holographic instrument will be analyzing.The hardware system of off-axis digital holographic particle detection instrument which is based on Sagnac interferometer will be designed and built.2.Holography has two parts which are the recording of wavefront and the reconstruction of wavefront.The reconstruction process of digital holography is done on a computer.This progress mainly uses the principle of scalar diffraction.The reconstruction process of the hologram is simulated on a computer with MATLAB in this principle.There are three methods for numerically reproducing holograms,namely Fresnel transform method(FTM),angular spectrum method(ASM)and Huygens convolution method(HCM).Not only holograms has been created with MATLAB and reconstruction using three methods,and their advantages and disadvantages has been compared based on the results.Besides it,some numerical techniques such as removal of twin images and numerical focus has been simulated with MATLAB.3.The holograms of the calibration plate,the resolution plate and the standard particle has been reconstructed in combination with the experimental instrument and the holographic principle.The system’s control program has been designed with Qt and Visual Studio and the camera’s SDK.Besides it,a complete set of experimental system software has also been designed.The parameters of camera can be set by the software of system and experimental results such as reconstructed images can be obtained in real time.The experimental results show that the off-axis digital holographic particle detection system can detect and reconstruct particles in water and air,and obtain the approximate size according to the system calibration.By the way,the structure of this instrument is simple and the cost of it is low,and the integration of it is stable.