Design And Experiment Research On A Small-size Streak Tube With High Luminance Gain

To observe ultrafast phenomena in the fields of strong laser physics,plasma,laser fusion,ultrafast chemistry and biology,ultrafast spectroscopy and optical communication,it is necessary to development ultrafast diagnosis technology with the ability of‘micro-catch-fast'.Streak camera is the only linear diagnostic instrument with both femtosecond-picosecond temporal resolution and micro-scale spatial resolution which can provide spatial-intensity-time information or spectral-intensity-time diagnostic parameters which means to detect ultrafast processes under extreme conditions.It is of great significance for basic frontier scientific research and upgrading of innovation ability.Also,it is an indispensable diagnostic tool in national strategic high-tech research such as inertial constraint fusion.At present,the design of traditional streak cameras mainly focuses on the high temporal resolution,spatial resolution,and all of them are almost image-amplifying streak tubes.These types of streak tubes have some shortcomings,such as low gain,low spatial resolution of the edge in slit direction,large volume and weight.In this paper,a small-size streak tube is designed and developed,which has the advantages of high luminance gain,large working area,high dynamic range and high edge spatial resolution.As the core component of the streak camera,the performance of the streak tube determines the detection performance of the streak camera.In this paper,the factors that affect the spatial resolution,temporal resolution and luminance gain of the streak tube are analyzed comprehensively.On this basis,a small-size streak tube with high luminance gain is proposed.It is designed with spherical photocathode,spherical slit accelerating electrode,spherical phosphor screen and multi-folded deflection plate.Also,we shift the optimum image point away from the center of the photocathode to improve spatial resolution on the whole cathode,especially in the edge.Firstly,the structure of spherical photocathode and spherical phosphor screen is helpful to reduce the differences of the optical path and to reduce the aberrations in off-axis points.The method of central electron beams under-focusing,edge electron beams over-focusing and optimum image point offset the cathode center is adopted to further improve the spatial resolution of edge and increase the effective working area.Secondly,the slit electrode can provide accelerating electric field,further improving the energy and momentum consistency of photoelectrons generated from the photocathode.High energy electrons can reduce the transit time of the photoelectrons in the streak tube and improve the temporal resolution.Otherwise,the slit electrode can provide anisotropic electric field,which can increase the minimum diameter of electron beam spot,thereby weakening the space charge effect and increasing the dynamic range of the streak tube.Compared with the mesh accelerating electrode,the slit can avoid the electrons to generate secondary electrons,which is helpful to reduce the background noise of the streak tube.And,the slit electrode has a higher electron transmission,which is useful for improvement of the luminance gain of the streak tube.Furthermore,the multi-folded deflection plate is adopted to ensure a high deflection sensitivity and a large deflection distance without photoelectrons being intercepted,further reducing the power of the deflection system.Finally,the theoretical design results are as follows.The length of the streak tube modeled is only?40 mm×140 mm,the static spatial resolution is higher than 25 lp/mm,the dynamic spatial resolution is higher than 15 lp/mm,the temporal resolution is better than 54.6 ps,the deflection sensitivity is 17.6 mm/kV,and the magnification is only 0.76.On the basis the small-size streak tube designed,the temporal distortion and aberrations are systematically studied.The dependence of the spatial resolution and the temporal distortion on the radius of curvature of photocathode is analyzed.The results show that the small-size streak tube with flat photocathode has a positive temporal distortion.The temporal distortion gradually changes from a positive value to a negative one while we reduce the curvature of photocathode.And,there is an optimum curvature radius,which obtains a minimum temporal distortion and high spatial resolution.Thus,the small-size streak tube with spherical photocathode and screen can greatly improve the bending degree of the slit scanning image and detection accuracy.Based on the theoretical design,a small-size streak tube with high luminance gain is been successfully developed.And,a static test system has been designed and built to analyze the radiation,image and gain performance of the small-size streak tube.The results show that the luminance gain is higher than 12 which is much higher than the5200_XIOPM streak tube,the luminance photocathode sensitivity is 178?A/lm.The photocathode radiation sensitivity and radiation emittance gain is 38.11 mA/W and18.82 with the wavelength of 550 nm.Also,the spatial resolution and magnification in slit direction is higher than 20 lp/mm and 0.76,separately.A miniaturized streak camera system was developed for the design of small-size streak tube with high luminance gain.For the whole streak camera system,we designed static and dynamic experiment scheme.Importantly,the corresponding experimental test system are built to evaluate the performance of the small-size streak camera.The results show that the temporal resolution is higher than 54.6 ps.The static and dynamic spatial resolution is 15 lp/mm and 10 lp/mm@T_screen=50 ns.The dynamic range is345:1@54.6 ps.