Research On Digital Holographic Lensless Microparticle Imaging System

Digital holographic imaging technology plays an important role in fields of information security,interferometry,particle field detection,and biological cell imaging.However,viewing the laser as the light source,the traditional digital holographic imaging technology requires the collimation and expansion,high cost,the strict mechanical structure,the complicated and cumbersome of the driving equipment,and multiple lenses.And the size of the particles observed in experiment is close to the dust in the air,which has a negligible effect on the results.Therefore,combining in-line digital holography technology with lensless imaging technology,a digital holographic lensless imaging system with portable and low cost based on LED has been designed in this paper.In this paper,the system using LED as the light source avoids the speckle noise caused by the laser.And the LED has the advantages of simple structure and easy integration,which greatly enhances the portability of the system.The system using in-line holographic imaging technology avoids the disadvantages of complicated optical path and high mechanical requirements for the system caused by off-axis holographic imaging technology;The system using the lensless imaging technology well avoids the effects of dust on the results.Secondly,three typical reconstructed methods have been summarized,in which the method of convolution reconstruction can eliminate the influence of other factors on the reconstruction of pixel size,which make spectral filtering easy and measuring microparticles more suitable.Therefore,the method of convolution reconstruction has been used to reconstruct images in this paper.And the microparticles in the image has been automatically counted using the threshold segmentation method based on region image segmentation in this paper.Finally,the optimal observation imaging conditions of the system have been exploredbytheoretical analysis,experimental verification and computer simulation,in which the blue light source with wavelength of 465 nm,half-wave width of 15 nm and divergence angle of110° was selected as source;a black-and-white camera of 2.2 ?m×2.2 ?m was selected as CMOS;and a microplate with a pore size of 75 ?m was selected as the microplate.In this paper,the diamond particles are used as samples in experiments,and the hologram images of the samples was collected by the designed system,then the samples images were reconstructed and the samples number in the images was automatically counted.Comparing the reconstructed image and its particle number with the raw sample image and manual counting respectively,It is concluded that the field of view of the digital holographic lensless imaging device designed in this paper is 20 times that of the microscope field under the objective lens of 10 times,the resolution of the system was 2--4?m.The system automatic counting method and the manual counting method have an error of only 6.3%.ensuring the rationality and feasibility of the system.