Line focal X-ray source imaging

Abstract

High spatial coherent and bright X-ray beam is necessary condition for acquiring high quality radiography image. However, traditional X-ray tube can only provide high flux X-ray light or high spatial coherent light. In general, X-ray photons are generated by using energetic electrons with several tens or even hundreds keV to hit a target. Unfortunately, over 99% electron energy are converted into heat rather than the energy of X-ray photons. Thus, the heat dissipation of the target restricts the emission power and radiation flux. Increasing the emission area of X-ray can relieve the heat dissipation, but it would bring another serious problemlow spatial coherence that is in inverse proportion to emission area or focal spot. In order to solve the conflict between brightness and spatial coherence, an X-ray source with one-dimensional coherence is proposed in this work. The new X-ray source has a special focal spot where one side is small enough to ensure the spatial coherence and the perpendicular side is big enough to provide sufficient X-ray flux. In the direction of long side, the long size of focal spot will result in losing the image details. Consequently, an algorithm of superposition and rotation, in which many images with different rotation angles are added together, is proposed to retrieve the lost information. On the other hand, the spatial transfer function of superposition is analyzed in the frequency domain, and the result shows that the method of superposition can transfer more components of frequency than single image. Based on a traditional X-ray tube, a line focal spot source is designed and fabricated. Two series of experiments are performed for different destinations. After 17 images of a chip with different rotation angles and the line focal spot are collected, those images are rotated in the reverse direction and added together. The image of superposition clearly presents some details which are invisible in one of 17 images. At the same tube voltage and for the same object, some comparative experiments with micro-focus source, line focal spot source and normal focal spot source are presented. Compared with traditional X-ray tube, line focal spot source can provide high-resolution image. In the aspect of image visibility, the new source has definite advantages compared with micro-focus source, despite no improvement in imaging resolution. Finally, the reason for the difference in imaging resolution is discussed from the aspects of spatial coherence and light flux.