X-ray imaging Fresnel zone plates and fabrication

In order to investigate the principle and fabrication technique of Fresnel zone plates(FZPs),a diffractive optical element used in X-ray imaging with the best resolution currently is presented.A theoretical analysis of the spatial resolution depending on the outermost zone width is given.An analytical expression of the diffraction efficiency in terms of thickness and X-ray refractive index of the zone plate is also provided.Electron beam lithography combined with X-ray lithography is employed to fabricate FZPs.Experimental results indicate that the outermost zone width is 150 nm and the aspect ratio is 4,which satisfies the X-ray imaging system requirements of high resolution,high aspect ratio as well as high precision.