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.     

一种高速多通道光纤阵列光开关

为了对短时间大视场一维光强信息进行采集,采用编码转换技术和自聚焦透镜矩形阵列设计了光开关,用小口径电光晶体实现了大视场的测量.采用MOS管级联的高压同步电路,使得系统具有结构紧凑、性价比高、寿命长等优点.实验结果表明:开关选通时间100±5 ns,前后沿小于25 ns,消光比1 100∶1.     

单色平面波从各向同性介质入射到晶体界面上折射波的求解方法

从麦克斯韦方程组出发,结合旋光晶体的物质方程以及单色平面波从各向同性介质入射到晶体界面时电场的连续性边界条件,通过晶体主轴坐标系和界面坐标系的坐标变换,推导了任意入射方向的单色平面波在晶体界面上的折射方向的求解公式,进而利用所得的折射方向求解晶体中折射波的电场本征模、电位移矢量本征模和光线方向。该方法以波动光学和晶体的物理性质为理论基础,推导过程没做近似,对双轴、单轴和各向同性晶体以及晶体是否具有旋光性都适用,并可通过计算机编程求出精确的数值解。