High-Speed Coaxial Digital Holography System Research And Particle Field Detection

The atmosphere contains a large amount of liquid and solid particles,both man-made and naturally occurring.Atmospheric particles play a key role in the health of the weather,climate and living things.Therefore,accurate measurement of atmospheric particles is of great significance.Using a high-speed CCD or CMOS camera instead of a normal area array camera,dynamic atmospheric particle hologram recording can be realized in a short time interval to avoid the occurrence of motion smear.The analysis of holograms by means of digital image processing technology can measure the particle diameter,spatial distribution,motion trajectory,velocity,sphericity and other parameters.Digital holography has many advantages in particle measurement.It not only has a simple and stable device structure,but also can image and distinguish laminated particles in three dimensions.In this paper,the digital holography technology is used to conduct experimental research on the measurement of atmospheric particles.The main work contents are as follows:Explain the basic theory of digital holography technology,and compare the advantages and disadvantages by experimental verification of three kinds of reproduction algorithms.In order to avoid motion smear when shooting dynamic object holograms,a high-speed coaxial digital holography system was designed and built.For the noise introduced during the hologram recording process,how to remove the hologram background noise and how to suppress the zero-order diffraction term of the coaxial hologram are discussed.In order to complete the acquisition of particle geometry parameters and motion parameters,the coaxial digital holographic measurement method was analyzed in combination with the experimental device,and the particle size,spatial position,velocity and sphericity were measured by simulation experiments on standard particles.The selection of the reproduction interval causes the error of the position measurement of the particles in the optical axis direction.On the basis of the original device,the twoviews recording of the hologram is realized by adding the mirror.The coordinates of the particles along the optical axis will be determined by the position of the mirror and the position of the mirror image,thus the measurement accuracy of the particles along the optical axis coordinates is improved.