Control Technique Research On The Range-gain-control Gated PMT Detection System

This paper investigates the control technologies of range-gain-control gated PMT detection system. It is aim to make breakthroughs in key technologies of the range-gain-control gated PMT in underwater laser target detection applications and to provide technical support for the development of the prototype of the underwater green-blue laser target detection system to meet the urgent needs of target detection at deep water. The key technologies studied here also can be used to other underwater target detection and imaging systems.The range-gain-control gated PMT detection system involves a wide range of technologies with many challenges to be solved, such as range gate and gain controls of PMT, high precision control of time delay, and interference suppression in weak signals. Through theoretical analysis and experimental study, the main content and work done in the paper are as follows.(1) The study of the range gate and gain control technology of PMTIn order to extract the useful underwater target signal, it is necessary to use the range gate technology to suppress the strong signals reflected from the sea surface and the water body. A range-gain-control gated PMT method is presented for this purpose through the applying of a nanosecond gating pulse and a high voltage gain controlled pulse to the PMT simultaneously. The PMT detection system based on this method is designed and the validity and feasibility of the ttechnology is checked through initial experiments. The results show that this method can complete the aim of the gate and the gain control of the PMT.(2) The study of the high precision time delay technologyAccording to the principal of the range-gain-control gated PMT detection method, the pulse widths of the gate and gain control pulses must can be adjust to meet the time sequence requirement of the gate and gain control purpose. The time delay circus and the pulse width control circus are designed. The measured precision of the time delay circus is less than100ps and the minimum width of the controlled pulse is10ns. The high precision time delay circus is applied successfully in the underwater laser target detection system.(3) The study of the interference suppression technologyIn the range-gain-control gated PMT detection system, the width of the output target signal is in ten nanosecond order and the amplitude of the output target signal is in the range of tens of millivolt to hundreds of millivolt while the amplitude of the interfering signal can achieve several volt orders. Thus, the extraction of the useful target signal is the problem of the extraction of weak ultra-fast signals in the big interference. The interference signal can also affect the control of the gate and gain pulses and even affect the time sequence of the gate and gain pulses. The sources of interfering signal are analyzed and discussed. The designed time delay circus is used to separate the target signal from the interfering signal. A special circus is designed to suppress the interference signal.(4) The experimental study of the control technologyThe performances of all the sub systems of the detection system and the output properties of the control system are studied experimentally. The image reconstruction is also studied. The special signal acquisition and process method is presented through the analysis of the time sequence characteristics of the return target signal.The study results of this paper could provide some assistance to the development of underwater laser target detection systems.