Imaging Technology Based On Time- Correlated Single Photon Counting

Time-correlated single photon counting is a type of detection technique for low-level signals.It records the counts of reflected photons which is proportional to intensity,instead of the traditional analog recording.The detection precision of this technique could reach to photonlevel with picosecond resolution.So it is of great value to research the laser imaging technology based on time-correlated single photon counting.The background,application and evolution of the time-correlated single photon counting technique and laser imaging technology are presented in this paper.And analyzes the principles of the two technologies and performance of traditional imaging system.Then the imaging system and system performance based on time-correlated single photon counting are analyzed in detail.The maximum work distance of this type imaging system depends on light intensity,transmission loss of atmosphere and receive aperture,and the major factor of which is the first one.The imaging vertical resolution only relies on time jitter of the whole system,which consists of pulse width,time jitters of detector and circuit control system.In this paper there are two imaging system are designed and constructed,one of which is bistatic system and the other is mono-static system.With theoretical analysis of both systems,it is concluded that bi-static system with simple structure has larger field of view,strong collection of photons but a lower signal to noise ratio.There is an internal reflection because of complicated optical structure in mono-static system,so that a delayer should be added to remove influence of internal reflection.This system has weak collection of photons for a smaller field of view,while the most practical value is that it could work in the conditions of light on with a higher signal to noise ratio.Ranging experiment and a series of imaging experiments are presented in this paper.It is found that the vertical resolution is 250 ps,which is the real value of the total system.And the precision of results is mm level through 40 s ranging experiments.In the imaging experiments,through the quantitative analysis of the peak signal to noise ratio and mean absolute error,we found that both system image with photon counts which depend on long scan time.The results show that mono-static system is more practical.Aimed at the disadvantage of long scan time,a new imaging system called first photon imaging system is proposed in this paper.It only records the numbers of pulse before the first photon is detected and flight time of the detected photon at each pixel.After analysis of image noise from traditional systems(bi-static system,mono-static system)and first photon imaging system,median filter algorithm and sparsity poisson intensity reconstruction algorithm are chosen to improve image quality.The quantitative analysis results indicate that median filter algorithm works better on images from traditional system than first photon imaging system,and first photon imaging system,a higher image quality could be obtained by sparsity poisson intensity reconstruction algorithm.