Research On Key Technologies Of Gated Image Intensifier Framing Camera

Ultrafast diagnostic equipment is an indispensable research tool in international cutting-edge technology and frontier scientific research.For example,Inertial Confinement Fusion(ICF)occurs in extremely short time(?10^-9 s),extremely confined space(0.1-1 mm),extremely high temperature(100 million degree)and extremely high density(300 g/cm³)and other extreme conditions.Therefore,its physical process can only be detected by diagnostic equipment.Traditional ultrafast diagnostic equipment,such as streak cameras,has a time resolution of sub-picoseconds,but does not have a two-dimensional spatial resolution capability.Travling wave gated framing cameras have space-time resolutions of up to?35 ps and?20 lp/mm,repectively.But the detection range of this diagnostic equipment is limited to the X-ray bands.This dissertation carried out the theoretical and experimental researches on the gated image intensifier framing camera.The gated image intensifier framing camera has high temporal resolution,two-dimensional spatial resolution,wide spectral response,stability,reliability,and flexibility and other advantages.Therefore,it has promoted the research of ultrafast physical processes into a new stage.In this thesis,starting from the two basic problems"imaging"and"control",systematic research work has been carried out on the key technologies of gated image intensifier framing camera.The main research contents of this thesis are as follows:1.In response to the requirement of high-speed gating,adjustable gate width and high repetition rate of gating of framing camera,in order to address the problems of image intensifier gating based on avalanche technology are often limited to fixed pulse width and low pulse repetition rate,an image intensifier gating circuit based on MOSFET devices has been demonstrated at our lab.In this thesis,combined with the design of totem-pole output(TPO)and separated control,the formation of the leading and trailing edges of the pulse is independently controlled to realize the continuous adjustment of the output pulse width.The method of providing gate current pulses to MOSFET devices is used to intervene the Miller effect during the turn-on and turn-off transition,in this way,the switching time is reduced to the order of nanoseconds from microsecond under high voltage condition,achieving the ultimate switching speed of the selected device.Optimum switching is obtained by designing to achieve maximal pulse current and precisely imposing fixed delays between the driving pulses to control the gate voltage.In this way,it is possible to accelerate the switching speed without demanding expensive components and increasing complexity.The results show that the designed module is capable of generating pulses of adjustable pulse width from 3 ns to D.C.operation with 1 ns switching time,a continuous repetition rate up to 300 kHz,and a burst repetition rate up to 4 MHz.2.A photocathode gating model based on the Finite Integral Technique(FIT)is built.For the first time,the model is designed in a numerical way to solve the dynamic electric field distribution in the 3D space between the photocathode and microchannel plate(MCP)input face.The gating speeds and gating patterns of image intensifiers are studied,taking the sheet resistance of photocathode as an independent variable.Theoretically guide the selection of clectric conductive underlayer of the photocathode.The simulation results show that when the photocathode sheet resistance is?10⁶?/sq,the turn-on time of a?18 mm image intensifier optical gate is?100 ns,and show an iris turn-on vehavior;while the photocathode sheet resistance is?100?/sq,the turn-on time of the optical gate is obtained in less than 1.2 ns,and the iris effect is greatly reduced.An optical gate experimental research platform was established,a?18 mm image intensifier without metallic underlay was analyzed for optical gating,the image intensifier responded with a turn-on time of 98 ns and a turn-off time of 112 ns,and produced an strong iris effect.A?18 mm image intensifier with metallic underlay photocathode was characterized for its optical gating time under an ultrafast gating mode of operation,the image intensifier responded with a turn-on time of 1.0 ns,a full-on time of 3.3 ns,and a turn-off time of 0.4 ns,giving a shortest total optical gate of 4.7ns.The iris effect is great reduced.The experimental results are in good agreement with the simulation results.3.For the first time,combining the Finite Integration method,Particle In Cell(PIC),Monte-Carlo(M-C)method,the image intensifier is designed in a numerical way to optimize the spatial resolution of the image intensifier.Introducing the Furman secondary electron emission model,electron multiplication process in the MCP multi-channel is simulated.The structure and accelerating voltage parameters of image intensifier are optimized.The optimized front and back proximity distances of the image intensifier are 100?m and 500?m,repectively.The optimized photocathode and phosphor screen voltages are-200 V and 6000 V,respectively.The optimized channel length of the MCP is 275?m,channel diameter is 5?m,the bias angle is 8°.and the penetration depth of the input and output electrodes are 5?m and 10?m,respectively.With a bias voltage of 900 V,the spatial resolution under the initial conditions is 34lp/mm@MTF=10%,while the optimized spatial resolution reaches 64 lp/mm@MTF=10%.4.The quantitative characteritics between bias voltage and image intensifier optical gain under different lighting conditions are studied.The measurement methods of image intensifier optical gate,spatial resolution of intensified camera system in D.C.and gating operation are studied.The performance evaluation systems for framing camara performance were established.The measurement results are as follow:the spatial resolution of the intensified camera system in D.C.operation reaches 32 lp/mm@CTF=32.99%,while reaches 28.5 lp/mm@CTF=25.45%in gating operation.5.The fluorescence lifetime imaging experiment is used to test the nanosecond gated image synchronization and acquisition performance of the intensified camera system.The image acquisition,synchronization and stability of the system are tested.The measured lifetimes of the three fluorescence dyes Rhodamine 6G,Rhodamine B,and Rubrene are?4 ns,?2 ns,and?9 ns,respectively.The results are in good agreement with typical values.