Research On The Key Technology Of Single Photon Imaging Based On Position Sensitive Anode

The intensity of light signals that need to be analyzed is often very weak with short duration in the research of high energy particle tracking,solar-terrestrial space exploration,biomedical development,et al.These light signals contain only a limited number of photons.Thus single photon imaging detection has become the research hotspot in these fields.The single photon imaging technology based on the position sensitive anode can reconstruct the image of weak radiation target within a certain integration time with high temporal and spatial resolution.It has been widely used in the detection of deep-space ultraviolet,X-ray and high energy particles.Research on the position sensitive anode in China has started quite late than foreign countries.The key parameters such as imaging spatial resolution and counting rate are far less than those abroad so far.To break the backward situation of domestic single-photon imaging technology for position sensitive detectors,a novel single-photon imaging system based on capacitive anode and the inductive charge readout method is studied and constructed in this paper.It has the advantages of simple fabrication,high counting rate,and it is expected to improve the signal to noise ratio further and achieve higher spatial and time resolution.In this paper,three key technologies of the system:electron multiplication,charge induction,and capacitor anode are theoretical studied.Effects of anode parameters on imaging quality are clarified.Furthermore,the feasibility of high spatial resolution and counting rate using capacitive anode single photon imaging technology is verified by a prototype.The main work accomplished in this paper includes the following aspects:1.A simulation model of microchannel plate(MCP)with reflective photocathode is established and used to simulate the trajectory of photoelectrons emitted from the photocathode.Based on the analysis of the photoelectron trajectory,a method for measuring the electronic gain of MCP with reflective photocathode is proposed.This method is used to test the electron multiplication gain of MCPs with different parameters.Finally the MCP structure parameters and cascading modes which meet the single photon detection requirements are obtained.2.A charge diffusion model of electrons in the inductive resistance layer is established based on the charge induction readout mechanism.The dependence of the distribution of the induction charge on the anode on the dielectric constant,the thickness of the substrate and the resistance of the resistance layer is studied.According to this,the charge loss can be effectively reduced and the signal to noise ratio can be improved.The induced current generated by the moving electrons on anode output conductor is calculated based on the Ramo theorem.3.Analysis shows that preamplifier noise is the main factor affecting the spatial resolution of the capacitive anode single photon imaging.A capacitive anode readout model based on discrete element method is established and used to calculate the effects of capacitance ratio C/C_w,C/C_d,(N-1)C/C_p(N is the number of nodes per row of the anode)on the linearity of anode recovered image.Results show that the root mean square nonlinearity of the recovered image is 0.04%when C/C_w is greater than100,C/C_d is greater than 1 and(N-1)C/C_p is less than 0.1.The calculated results are verified by experiments.4.A single-photon imaging system based on capacitive anode is built based on the theoretical results.The dependence of system imaging spatial resolution,counting rate on UMCP(MCP working voltage)and UM-a(potential difference between MCP output surface and the induction layer)is studied.Results show that the spatial resolution of the induction readout capacitance anode single photon imaging system is better than 250?m,and the counting rate is about 6.5kcps.