Study Of Optical Super-oscillation Elements Design And Applications In Imaging

Optical imaging technologies have driven the revolution of the human society,and they have profound influence on various disciplines,such as the Biology,Physics,Chemistry,Medicine,etc.Diffraction,as an essential property of the light,gives a fundamental constraint on the resolution of imaging systems.In the field of optics,it is always a hot topic to overcome the traditional diffraction limit and to develop the super-resolution imaging methods.With the development of advanced optical imaging theory,it has seen great achievements in fluorescence microscopy,near-field scanning imaging and other fields.However,those methods could not find applications for observing far-field but inoperable targets.Recently,in the field of far field optical imaging,researchers have proposed the design ideas and technologies of a new type of optical super-diffraction element,namely the super-oscillation element,which could realize far field super-diffraction imaging needless of the evanescent wave extraction and the fluorescence labeling.Using those methods,the Abbe diffraction limit has been effectively broken,which has very important scientific research values in the field of advanced optical imaging.In this Ph.D.dissertation,we mainly study on the design of the super-oscillation element,as well as its applications for imaging.This study could have important theoretical and practical reference values in micro & nano lithography,medical imaging,precision measurement,optical storage,etc.The main research contents and innovative research achievements of this paper are as follows:(1)Based on the binary separate-type super-oscillation elements(SOE),a far-field super-diffraction imaging method with small field-of-view(FOV)is proposed,which could effectively overcome the technical difficulties existing in the present super-diffraction imaging systems such as the small working distance,serious off-axis imaging distortion,etc.Innovations of this method can be generalized as: firstly,using a separated-type SOE design method,a distortion-free off-axis imaging within a small FOV could be realized.Secondly,based on the scalar angular spectrum theory,a nonlinear optimization model for SOE designs is built,which could effectively overcome the problems of complex boundary conditions and incomplete optimization remaining in the traditional linear optimization methods.Experimental results demonstrate that,using a 632.8 nm laser beam,a distortion-free super-diffraction focal spot could be realized at a FOV of 1.5°,and the full width at half maximum(FWHM)of the focal-spot could be shrunk to 0.31?/NA,where the resolution has 38% improvement over the diffraction-limit system with the same numerical aperture.(2)A hybrid SOE design method is proposed for non-scanning super-diffraction imaging.Firstly,for the case of small FOV and short focal depth in the snapshot imaging of those present super-diffraction imaging systems,based on Alex's super-directive antenna design method,the Chebyshev polynomials are utilized as a basis set for constructing the ideal super-diffraction wave-front.Then,by appropriately restricting the transmission of the central part of the SOE,a hybrid SOE optimization model is built.The imaging simulation results demonstrate that with the help of the hybrid SOE,a greatly axial extended needle with continuous super-diffraction characteristics is yielded in the imaging plane,which has 120% improvement in sidelobes suppression ratio over the present super-diffraction imaging systems.Besides,the longitudinal depth of focus could reach to 3.13?/NA,which allows a large imaging tolerance in the axial displacement of the object,making it available for the study of the real-time and wide-field super-resolution imaging systems.(3)An incoherent non-scanning super-diffraction imaging(N-SDI)system is proposed and constructed.Different from the coherent scanning imaging mechanism in the present super-diffraction systems,the innovations and the superiorities of the N-SDI system are obvious.Firstly,a binary amplitude-phase type hybrid SOE is processed by ion beam etching technology,getting rid of the polarization dependence in current wavefront modulation schemes using spatial light modulators;Secondly,the incoherent illumination mechanism is used instead of the traditional coherent illumination mode,which could effectively suppress the unwanted interference term coming from different parts of the object,and the imaging noise could be greatly reduced.The imaging experiments on complex targets are conducted,which demonstrate the feasibility and effectiveness of this system in far-field non-scanning super-diffraction imaging,where a resolution of 0.35?/NA could be obtained,which has 30% improvement over the conventional diffraction-limit system with the same NA.