分幅变像管动态空间分辨率的标定

Calibration of the dynamic spatial resolution of framing image-converter

为了提高激光惯性约束聚变实验二维成像诊断的精密化程度,提出了分幅变像管动态空间分辨率的标定方法.标定原理是以直边函数为物,经光学系统成像后求解系统的调制传递函数,从而获得系统的空间分辨率.在神光II装置上利用八路激光打靶产生1—3.5keV能区的连续X射线标定源,照射高Z刀边材料,并成像到分幅变像管阴极上,分幅变像管采用脉冲选通工作模式获得动态像.对分幅变像管采集的动态图像进行处理得到系统的调制传递函数.根据调制传递函数为0.1时对应的空间截止频率,得到系统的空间分辨率为20lp/mm.根据分幅变像管的动态空间分辨理论,计算系统的极限空间分辨率为22.8lp/mm.标定结果略低于极限空间分辨率,与理论基本吻合.根据传统标定方法得到该分幅变像管的静态空间分辨率为22lp/mm,比动态空间分辨率略高.在二维成像诊断时,分幅变像管工作于动态选通模式,故动态空间分辨率的标定结果更能真实地反映其成像诊断能力.

In order to improve the two-dimensional imaging diagnostic accuracy of inertial confinement fusion（ICF） experiment,a calibration method of the dynamic spatial resolution of X-ray framing image-converter（XFIC） is proposed.When an object with straight edge function is projected onto the photocathode of XFIC as an input,edge spread function can be obtained by recording an image of the XFIC output.The first derivative of the edge spread function produces the line spread function（LSF）.Then the modulation transfer function（MTF） of the system can be worked out by Fourier transform of the LSF.Therefore,the spatial resolution can be deduced.According to this theory,the spatial resolution of XFIC can be obtained.Based on SG-II laser facility,the calibrating X-ray source is generated by 8bundled lasers bombarding the target.High-Z knife-edge is irradiated by the X-ray and imaged on the photocathode of XFIC,and then a dynamic image is obtained as the system works in the gating mode.By handling the dynamic image,the LSF of XFIC is given by analyzing the edge image.Then the MTF of the camera can be indicated by the Fourier transform of the LSF.When the MTF is 0.1,the corresponding spatial resolution of the imaging system is 20 lp/mm.According to the dynamic spatial resolution theory of framing image-converter,the extreme spatial resolution is 22.8lp/mm.The calibration result agrees with the theoretical results.By contrast,the static spatial resolution of the same X-ray framing image-converter calibrated by the traditional method is presented here.The calibrated static spatial resolution is 22 lp/mm,a little higher than the dynamic one.During the two-dimensional imaging diagnosis,the X-ray framing image-converter works in the dynamic gating mode,thus the calibrated dynamic spatial resolution can be more truthful to reflect its imaging diagnosis ability.