| Single-photon counting technology is a detection method for extremely weak light.It uses pulse discrimination technology and digital counting technology to identify and extract extremely weak signals,and theoretically obtain the information of a single photon.As a kind of single-photon detectors,photon counting imaging detectors based on MCP and position-sensitive anode have extremely high sensitivity and spatial and temporal resolution capabilities,and have been widely used in space astronomy,biofluorescence,quantum information and high-energy physics,etc.In view of the weak and extremely weak light detection requirements,this paper aims to develop a cross delay line(XDL)photon counting imaging detector with large area and high temporal and spatial resolution.The main research contents and achievements of this paper are as follows:(1)The electron cloud transport process of the inductive readout detector was studied,including the electrons output from MCP,the arrival on the high-resistance Ge layer,the diffusion on the Ge layer and induce charges on the position-sensitive anode.The effects of different dielectric materials and thicknesses on the amount of induced charge were studied and experimentally tested,which provides theoretical guidance for the design of inductive readout position-sensitive anode,especially for maintaining the charge balance between electrodes.(2)Two types of delay line position-sensitive anodes were designed and fabricated:the collecting electrode in the same layer(No.1 anode)and the collecting electrodes in different layers(No.2 anode).Both anodes have a 4-layer electrode structure,but use substrate materials with different dielectric constants,respectively.The No.1 anode transmits the electrons collected from the surface layer to the lower delay line electrodes through plated through holes(PTH).The signal transmission electrodes cross multiple times,so the crosstalk between electrodes is relatively large(～8%)and the output pulse(FWHM)is slightly wider(～8 ns).The No.2 anode collected charges using a heterogeneous-layer induction readout method.The collector electrodes were located in different layers and the delay line unit was located around the anode,which better solves the problem of crosstalk between electrodes.The test results show that the crosstalk between anode electrodes is less than 1.5%and the anode output pulse width(FWHM)is about 4 ns.(3)The front-end circuit of the detector was developed,which mainly included a pre-amplifier circuit,a filter shaping circuit and a Constant-Fraction Discriminator(CFD)circuit.Using the developed front-end processing circuit and commercial TDC(Time-to-Digital Converter,TDC)module,an experimental test system for the delay line position-sensitive anode detector was assembled.The imaging performance of the two different delay line position-sensitive anodes was tested by the detector testing system assembled.The results show that the spatial resolution of the No.1 anode is up to 100μm,while there is a larger imaging distortion.The spatial resolution of No.2 anode is about 150μm and the imaging linearity is better.The imaging nonlinearity of this anode is<8%.(4)The vacuum tube body of the photon counting imaging detector responding to visible light band was developed.The detector adopts S20 cathode,with an effective area>?22 mm and MCP gain>10~6;The factors affecting the performance of the detector’s TTS(Transit Time Spread,TTS)were simulated by CST,including spacing between photocathode and MCP input surface,its voltage,MCP itself and MCP output-anode spacing and voltage,etc.The TTS of the inductive readout detector was experimentally tested by coupling the anode with vacuum tube body,and the results show that the TTS of the detector is better than 110 ps.The imaging performance of the detector was tested by coupling the delay line anode with the vacuum tube body:the dark count rate of the vacuum tube-packaged detector is less than 185 counts/s,the gain uniformity is good(<5%)and the spatial resolution is better than 180μm.(5)The developed photon counting imaging detector was initially applied to lidar experiments.In the scanning mode of photon counting 3D radar,the detector was applied in the existing experimental system and the instrument response function(IRF)of the system is 448 ps.Based on the non-scanning laser 3D radar system,the system IRF is about 2.2 ns.By using the system,the laser ranging experiment and the preliminary laser three-dimensional imaging experiment are realized. |
