Study On Imaging Conditions For LED-lensless Digital Holography

Lensless digital holography is a technology which is based on the interference and diffraction of light,and uses photoelectric sensors to record the interference pattern of the object light and reference light,then uses computer to program reconstruction algorithm to obtain the object amplitude and three-dimensional phase information.Compared with traditional microscopy imaging technology,lensless digital holography has the advantages of rapid imaging and simple operation.Now it has become one of the research hotspots in cell counting,cell three-dimensional imaging,and portable imaging.However,there are still some deficiencies in the selection of imaging conditions.So in this paper,the selection of imaging conditions for lensless digital holography systems will be studied.Firstly,combined with the basic theory of lensless digital holography,the system is analyzed for multiple imaging conditions,such as photoelectric sensor,LED,microhole,the distance between the LED and the plane of the object to be measured and the distance between the plane of the object to be measured and the photoelectric sensors.For photoelectric sensors,the influences of sensor size,resolution and pixel size on holographic imaging results are analyzed.For LED,the characteristics of time coherence and influencing factors are analyzed.For microhole,the influence on the spatial coherence of light sources is analyzed.Finally,it focuses on analyzing the distance between the LED and the plane of the object to be measured,and the distance between the plane of the object to be measured and the photoelectric sensor on holographic imaging results.Secondly,the preparation work before the experiment is carried out,mainly including the introduction of the lensless digital holographic system platform used in the experiment,and the effectiveness and maneuverability of the experimental verification test platform.In this paper,a standard particle plate prepared from 10 μm diameter polystyrene particles(simulated cells)is used to perform holographic imaging experiments based on the experimental platform.The holograms of standard particles are successfully obtained,and the operability of the experimental platform and the imageability of the standard particles have been effectively verified,which is the premise and basis for subsequent series of related experiments.Furthermore,a series of experiments on the selection of imaging conditions are carried out.The main imaging conditions include the model and specification of the system electronic devices,the diameter of the micropores,the LED wavelength,the distance between the LED and the object to be measured,and the distance between the objects to be measured and the sensor.From the experimental requirements,the CMOS sensor parameters of multiple models are analyzed and compared.Finally,the CMOS sensor with the maximum size,the maximum resolution and the smallest pixel size is selected.According to the compact structure of the holographic system and the simple device,the LED with small size and small light emitting angle is inserted.The experiment of obtaining particle hologram with micropores of different diameters is carried out,and the quality of the reconstructed image is evaluated by means of signal to noise ratio and grayscale gradient.The results show that the imaging effect is best when the diameter of the micropore is 100-200μm.At the same time,the experimental investigation of the distance between LED and the object to be measured is studied.The results show that the larger the distance and the better the quality of the image,but based on the need of the miniaturization of the system,the distance range is more suitable than the 8cm.In view of the time coherence of LED,the experiment of obtaining the particle hologram using LED with different coherent length is carried out and compared.The results show that the imaging quality of the system is the best when the single wavelength LED is used.Change the distance between the plane of the object to be measured and the photoelectric sensor to carry out the experiment of obtaining the particle hologram.The result shows that the best effect is achieved when the recording distance of the system is 1 mm.Finally,this article integrates the parameters obtained by the above imaging conditions selection experiment study,and takes the blood cells as the experimental object to carry out its digital hologram acquisition experiment,to verify the validity of the imaging conditions selected in this paper.As a result,a better quality cell hologra m was successfully acquired and its amplitude information was reconstructed,resulting in a clearer cell image.Therefore,the research carried out in this paper will provide a useful reference for the construction of the subsequent lensless digital holography system,and it will help promote the development of related applications such as cell counting.