Defocus image restoration by an accurate optical transfer function of Fresnel zone plate in soft X-ray microscopy

High-resolution soft X-ray microscopy has been widely adopted for obtaining the three-dimensional structure of physical objects. However, the limited depth of focus may cause sample defocusing and, subsequently, lead to blurring of images. A defocused image restoration method was proposed based on an optical transfer function (OTF) of a Fresnel zone plate (FZP). Using this restoration method the defocused image of Siemens star was restored. The results show that the restoration method based on OTF is capable of suppressing the blurring effect and restore defocus images caused by defocusing of the object. Furthermore, related simulations have been carried out to demonstrate the effectiveness of this method in overcoming the limitations to focal depth and accomplishing three dimensional imaging of samples.