Xu Xiangyan

Research on large dynamic range streak camera based on electron-bombarded CCD

In order to detect the weaker on greater span of light signals, the dynamic range, spatial resolution, and the signal to noise ratio of the streak camera need to be improved to meet further diagnostic requirements in scientific area of materials, biology, information, semiconductor physics and energy, etc. Therefore, we design a streak camera with a larger dynamic range based on electron-bombarded CCD. Using the rectangle-framed electrode and electric quadruple lens in the streak camera can reduce its space charge effect and shorten the space charge interaction time by improving electron accelerating voltage to minimize the electron transit time. Using a back-illuminated CCD, which is based on the electron bombardment readout technology as image device to replace the traditional intensified CCD can shorten the chain of image conversion and greatly reduce the image degradation in the conversion of ultrafast diagnostic equipment. The signal to noise ratio, spatial resolution and dynamic range of the streak camera may gain improvement. Experimental results show that the static spatial resolution is better than 35 lp/mm and the dynamic spatial resolution is up to 20 lp/mm. Deflection sensitivity is 60.76 mm/kV and dynamic range reaches 2094: 1. Nonlinear scanning speed is 5.04%. EBS gain of the streak camera can be over 3000.

Design and Demonstration of Carbon Nanotubes(CNTs)-Based Field Emission Device

Since its discovery, carbon nanotube (CNT), possessing a series of particularly electrical and mechanical property as well chemical stability, has been considered as one of the most advanced electronics materials. A lot of research has been extensively carrying through on CNTs’ potential applications for instance, gas storage, quanta lead, electron device, catalyst carrier, and etc. Among its various applications, more talked is its application as field emission cathode (FEC) material to make large-area, full-colored and high efficiency displays or lighting devices (FEC-LED) because of its excellent field emission property. Compared with the other material of field emission cathode, CNT-FEC devices have a series of unique performances, such as higher field emission efficiency, lower power consume, lower cost, non pollute problem in its production processes, and so on. Those advantages come from the following physical and chemical mechanism: 1. CNT possesses so large aspect ratio in structure that the field enhancement factor CNT can reach 30000 to 50000 for single CNT, 800 to 3000 for CNT film, no mater what state , standing or lying they are. Therefore CNT is such an excellent field emitter that CNTFEC can easily provide necessary current under a lower drive voltage with much lower power consume. 2. CNT-FED workmanship is simply, the material cost is low. When the manufacture is enlarged, it can compete with other technologies of display or lighting devices in price. On the other hand there are still some theoretical and technical problems need to be solved before CNT-FED being get more competitive applications on the market, for example, its feasibility of a large scale production,full colored field, optimal structure design, spatial homogeneity, stability, lifespan, as well as its low cost fabrication technology. this chapter mainly concerns these problems mentioned and gives some elementary discussion in for our further understand of them, including:  The research on the field emission properties of CNT and computer simulation based on Fowler-Nordheims theory;

Femtosecond electron pulse compression by using the time focusing technique in ultrafast electron diffraction

We present a new model of an electron gun for generating subrelativistic femtosecond (fs) electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing electrode generates an electron energy chirp for bunching at the target. Without considering the space charge effects, simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode. Tracing and simulating large numbers of photoelectrons through Monte—Carlo and finite difference methods, the electron pulses with 1 ps can be compressed to 55 fs, which will allow significant advances in the field of ultrafast diagnosis.