Design Of Zone Plates And Their Diffraction Characteristics

The Fresnel zone plate (FZP) is a kind of beam-forming and focusing device, which has attracted great attentions in the last two decades for its achieved and potential applications in the fields of extreme ultraviolet imaging, X-ray imaging, imaging and focusing of atoms. As the refractive index is very close to unity for all materials at X-ray wavelengths, FZP plays a role of the most promising optical element in X-ray imaging. A lot of efforts have been made to develop the techniques of fabricating and designing FZP with the purpose of improving its spatial resolution down to nanometer. Many properties of the FZP have been studied, such as aberration, diffraction, and stigmatism. Some interesting work about zone plates, such as photon sieves and fractal zone plates, have been reported in recent years. Spiral zone plates for X-ray microscopy are fabricated to detect phase effects and isotropic edge enhancement. Spiral fractal zone plates for generating vortices are also reported. This thesis is devoted to design and study some new kinds of zone plates and their potential applications.In Chapter 1, the fundamental knowledge of FZP including focusing properties and fabrication process and a brief introduction to the research progress of FZP are given.In Chapter 2, experimental demonstrations of the diffraction and dispersion phenomena of part Fresnel phase zone plates (FPZPs) by employing a He-Ne laser beam and white point source of carbon nano material are reported. The experimental results have shown that a part square FPZP can behave like a complete circular FPZP, and a part circular FPZP has foci at 1/3 f and f, respectively. Some numerical simulations are performed. The simulations and the experiments have shown that the diffraction and dispersion properties of part FPZPs can be well explained by the different diffraction orders.In Chapter 3, a new type of square FZP with spiral phase for generating zero axial irradiance is proposed. Diffraction patterns of the zone plates with different generalized topological charges are given by numerical simulation, which also suggests their potential applications in generating hollow beams. The condition of the generalized topological charge that makes zero axial irradiance is derived and analyzed.In Chapter 4, we propose a kind of circular FZP consisting of alternate transparent and opaque zones with spiral phase. Focusing properties of this'zone plates with integer and fractional topological charges are studied. Numerical results show that doughnut hollow beams can be generated by zone plates with integer topological charges and can be controlled by the total zone numbers and topological charges. Asymmetric hollow beams can also be generated by zone plates with fractional topological charges.In Chapter 5, a series of new zone plates with moire fringes are obtained by means of overlapping two identical circular, elliptic, and hyperbolic FZPs and changing the scale of the FZP displayed on a computer screen. The diffraction patterns of this kind of zone plates with moire fringes are studied.In the last Chapter, we outline our works and point out some existed problems in our studies, which should be improved in our future work.