X光能点、放大倍率及针孔尺寸对空间分辨的影响

Effect of X-ray wavelength,pinhole aperture and magnification on spatial resolution

X光针孔成像是惯性约束聚变(ICF)研究中重要的诊断方法,对其点扩散函数的计算可用于图像重建和系统空间分辨的判断。对菲涅耳衍射公式进行了化简,分析了X光能点、针孔尺寸及放大倍率对针孔点扩散函数的影响。实验在保证成像能获得足够高信噪比的条件下,通过模拟获得在最佳空间分辨时所要的针孔大小、放大倍率和X光能点等参数。在流体力学不稳定性的静态样品定标实验中,通过模拟获得了针孔的调制传递函数(MTF),结合实验测量的结果反推获得分幅相机本身的MTF值。同时采用测刀边函数的方法获得了分幅相机本身的刀边函数,进而得到相机在各空间频率下的MTF值。两种方法得到的分幅相机MTF值一致,验证了通过菲涅耳衍射模拟X光针孔成像的可行性。

X-ray pinhole imaging is an important diagnostic tool in inertial confinement fusion （ICF）. The point spread function （PSF） of the X-ray pinhole imaging can be used to restore the initial image and estimate the spatial resolution. This paper analyzes relations among X-ray wavelength, size of pinhole aperture, magnification and also simplified Fresnel diffraction formula. The PSF of the X-ray pinhole imaging was derived numerically using Fresnel diffraction integral. Fresnel diffraction simulated the optimal pinhole aperture, X-ray wavelength and magnification with optimal spatial resolutions and an excellent signal-to noise ratio. The calibration of the sample was used to gain the modulation transfer function （MTF） of the whole framing camera imaging system, and Fresnel diffraction simulated the PSF of the pinhole imaging, so the PSF of the framing camera was deduced. We also obtained the PSF of the framing camera by measuring its edge function, the two results were unanimous and showed the method to stimulate X ray pinhole imaging by using Fresnel diffraction is feasible.