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Numerical and Experimental Study of the Super-resolution Imaging and Nanostructure Fabricating Based

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Tutor: BaiJinTao
School: Northwestern University
Course: Optics
Keywords: Stimulated emission depletion,Vectorial diffraction integral,Primaryaberrations,
CLC: O439
Type: PhD thesis
Year:  2013
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Abstract:
A number of techniques of nano imaging, fabricating, fluid velocity measuring based on the continuous wave (CW) stimulated emission depletion (STED) system have been studied by using vectorial diffraction integral theory and a self-made CW STED system in this Ph D project. It lays theoretical and experimental foundation for resolution improving and new application developing of the far-field super resolving technology.The core ideology of STED technology is to confine the point spread function (PSF) of the fluorescence to a sub-diffraction size with a certain structural depletion beam. Therefore,the spatial structure and the intensity distribution properties are a kind of dominating factors of the resolution.In this project, the theoretical model for focal field calculation of CW STED system has been built up based on vectorial diffraction integral theory which is applied for focusing light investigating in high numerical aperture system.The depletion focal patterns engineered by applying the variety of phase plates with different polarized laser are obtained in the calculation; the characters of the efficient PSF compressing STED structures, as well as the improvements on resolution, are analyzed and discussed in detail.. In addition, the primary aberrations cause the decline of the resolution. Therefore, the primary aberration effects, especially the combined influence of the primary aberrations on depletion beam have been studied by utilizing the theoretical model. The study is instructive for the insightful understanding of the key element of the STED technology.The STED technology has inspired new approaches for the far-field nano fabrication. In this project, a nanopillar/pore fabrication method based on a CW visible laser direct writing system derived from a CW STED system is proposed. In the experiment, a visible laser with center wavelength at532nm is modulated by a0-2Pi spiral phase plate to generate a donut-shaped exposure beam. The photoresist at the center of the focal spot will not be exposed due to the zero intensity dark core of the donut-shaped pattern. A kind of nanopillar structure will be obtained when a positive-tone photoresist is adopted, while nanopore structure will be fabricated when using a negative-tone photoresist in lithography. In the experimental fabrication, a kind of nanopillar array has been obtained successfully on a positive film with the pillar¡¯s diameter can achieve1/11of the incident wavelength, far smaller than the diffraction limitation. The transformation of the experiment results are explained reasonably with the multiple aberrations theory. This study has proposed and realized a novel, simple, efficient and cost-saving nanopillar/pore fabricating method with CW visible light.In the third part of the thesis, a STED system using CW lasers is built up and applied for the fluorescence depletion efficiency study. Moreover, the nonlinearly phenomenon that might be induced by the strong excitation and depletion field in some reagents are analyzed and discussed; it provides valuable references for resolution improving and the nonlinearly fluorescence effect studying in STED technology. In addition, the imaging of fluorescent particles has been obtained based on the CW STED system with the resolution achieving70nm. The velocity profile in nano channels also been measured by combining the system with laser induced photobleaching method, which will make a great contribution for the key technologies of lab-on-chip and nano sensing.In this project, the theoretical model for CW STED system has been built up for the study of the key techniques of the STED technology firstly. Then, based on CW STED system, a novel, simple and cost-saving nanopillar/pore fabrication method has been proposed. In addition, the depletion efficiency of variety dyes has been studied with a self-made CW STED system. The super resolution imaging and micro fluid measuring has been presented. In sum, this doctoral project provides some new thoughts and approaches for further improving the resolution and exploring the new applications of the far-field super-resolution technology.
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