Numerical Study On Zone Plate Diffraction Efficiency Improvement And The Imaging Of An Extended Source

In inertial confinement fusion,we compress the targets using high-energy laser or the x-ray produced by the laser.Hydrodynamic instability may occur during laser ablation and compression of the target,and this is also the key to the success of the fusion process.To diagnose the hydrodynamic instability of the target,the target is often diagnosed using X-ray backlit photography.Due to the strong penetration of X-rays,almost all materials used in the manufacture of optical devices in the visible light field cannot be used.Fresnel zone(FZP)plates can be used for X-ray imaging.However,due to its high-order diffraction and low first-order diffraction efficiency,it restricts its widespread use.This article has studied the X-ray imaging of FZP and mainly includes the following two aspects.The first part focuses on the disadvantage of the low diffraction efficiency of FZP and proposes an improved solution.On the basis of previous work,combined with the design ideas of the phase shifting stepped zone plate and the new technology of making the zone plate,a new type of high efficiency diffractive zone plate was proposed.The core idea of this kind of zone plate is to use different metal materials at the same thickness to make the transmittance function of the zone plate approximate the transmittance function of the ideal lens.First of all,a mathematical analysis of this zone plate shows that its diffraction efficiency is about 68.39%.Afterwards,the Matlab program was programmed to perform X-ray imaging studies on this zone plate,and compared the results with those of the amplitude-type FZP,and studied its focusing characteristics when the incident light is non-monochromatic light.The second part mainly deals with the study of the law of large-scale source imaging of FZP.In order to cooperate with the visible light band experimental verification,we used the same theory in the visible light field to simulate the FZP imaging results for large-scale sources,mainly on the effect of the extended source size and the spectral bandwidth of the light source on the resolution and contrast of FZP imaging.The results show that for a certain size of extended source imaging,the image resolution is not affected as the off-axis degree increases,but the contrast increases as the axis deviates from the optical axis.Changing the size of the extended source to observe the imaging conditions at the center of the field of view,it was found that as the size of the extended source increases,the resolution does not change and the contrast decreases.When the incident light has a certain bandwidth,the resolution and contrast decrease as the bandwidth increases.