Study Of Ultraviolet Photon Counting Imaging Detector Based On Cs₂Te Photocathode

Many celestial bodies in the universe emit weak ultraviolet radiation,and some celestial bodies emit ultraviolet radiation at some stages of their evolution.The detection of the ultraviolet emission is an important way to study the universe.With the development of UV detection technology,ultraviolet detectors have been widely used in these fields such as space exploration,military early warning,ultraviolet communication,criminal investigation and corona detection and so on.An ultraviolet photon-counting imaging detector is designed and studied in order to achieve two-dimensional image from ultraviolet light emitting body in this master's thesis.This kind of detector is mainly composed of photocathode,micro-channel plate?MCP?,wedge-strip position sensitive anode and position readout circuit.The photocathode can convert incident UV photons into photoelectrons,and the position readout circuit collects,transmits and processes signals from the anode and display UV image on computer's screen.To realize the UV detection in solar-blind region,we have developed a Cs₂Te photocathode UV detector with an operating wavelength between 200 nm and350nm.Firstly,the general structure and working principle of Cs₂Te photocathode UV photon detector are introduced,and the structure and function of each part of the detector are described in detail.Wherein the entrance window,a MCP stacks andthe output window are sealed hermetically to form a tube body.At present the sealed tube body has two kinds of structures according to the difference way of charge collection in anode,after the advantages and disadvantages of the two structures are analyzed,the method of inductive charge read out is adopted.Then,the performance parameters of several different cathode materials were introduced,and the Cs₂Te photocathode with good performance was fabricated by Te process.In order to reduce the influence of excess Cs and Cs compounds on the threshold wavelength,the Cs activation process is improved and the Te atoms are compensated to react with the surplus Cs atoms to form Cs₂Te,so as to reduce the visible light response.And then the main factors affecting the performance of the Cs₂Te photocathode were analyzed and the quantum efficiency and spectral responsivity were measured.Finally,according to the characteristics of the detector output signal,a position readout circuit based on high-speed analog-to-digital conversion?A/D?chip and FPGA is designed.The method uses a high-speed A/D chip?65MHz sampling rate?to acquire the peak value of the signal after point-by-point sampling to replace the expensive peak hold module in the original front-end analog circuit.This method without peak hold module employs high-speed A/D chip to acquire the peak value of input pulse signal point by point,so the signal can be collected and processed continuously in real time,and the photon counting rate of the imaging detector is evidently improved.Secondly,the composition and working principle of each part of the circuit are introduced in detail.At last,the imaging performance of the detector is tested,and the parameters of each part of the detector system are optimized by analyzing the acquired data and imaging results.