Investigations On Side-lobe-free Superoscillatory Light Fields

Due to the diffraction and dispersion effects of light,the imaging system has diffraction limit.The traditional resolution limit can no longer meet the needs of scientific researchers,how to break through the diffraction limit in essence is the primary problem of current research.Since the 21 st century,the spatial resolution has been mainly improved from the aspects of the near and the far fields.The near-field technology mainly collects evanescent waves that gradually decay on the surface of the object to obtain the fine structure of the wave field.On the other hand,far-field imaging is achieved by labeling objects with excited fluorescent molecules and then precisely positioning the fluorescence.However,the near-field technology is limited by the working distance,while the far-field technology requires special dyes,which cannot be widely used.During the exploration of improving the spatial resolution,the phenomenon of super-oscillation has entered the research field,under the condition that the light field is not dependent on evanescent field,the ultra-fine structure of the light field can be propagated to the far field without special dyes,which provides a new way for far-field imaging.Subsequently,a large number of far-field focusing microstructures using the super-oscillation effect were designed,although a focused spot can be obtained that breaks the diffraction limit,the spot is inevitably accompanied by highintensity side lobes,and the design requires complex algorithms to optimize the structure,this limits the potential applications of microstructures.Here,we design a superoscillating structure without the need of optimization algorithm.The superoscillating wave field generated based on the principle of sharp-edge diffraction can obtain a focused spot without sidelobes in the far field,which breaks the balance between the superoscillating main lobe and the accompanying side lobe.Therefore,this thesis investigates the generation one-dimensional and two-dimensional side-lobefree super-oscillating light fields.The specific content is:Firstly,a new principle for generating the wave field of the super-oscillation structure is proposed,namely the principle of geometric sharp edge diffraction.The high-frequency components induced by geometric sharp-edged diffraction are coherently superimposed in the propagation space to obtain a focused spot.Based on this principle,we designed a bi-moon-like sharp-edged structure.Firstly,the design steps and process of the structure are introduced.Next,the generation of super-focusing light field by the structure is studied theoretically and experimentally.A focused spot that breaks through the diffraction limit can be obtained in the center of the structure,and there is no side lobe accompanied in the y direction.We further obtain the phase map distribution at different positions during the propagation of the structure,and verify the superoscillating effect of the structure by measuring the phase oscillating frequency in the central region.Finally,it was found that the size and position of the focused spot are related to the size of the structural parameters.Secondly,on the basis of the one-dimensional side-lobe-free superoscillating light field,we design two pairs of moon-like structure in x-y space,its unique design makes the focused spot have no sidelobe in the two-dimensional direction.We use the fast Fourier algorithm to further verify the focusing characteristics of the structure and analyze the influence of the structure parameters.When the size of the structure increases in the same proportion,the same focused spot will be generated at a further distance,which will further promote the development of far-field super-resolution imaging.