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Ultrafast Nonlinear Spectral Characterization Of Low-dimensional Nanomaterials And Structures

Posted on:2020-07-14Degree:MasterType:Thesis
Country:ChinaCandidate:R Q WangFull Text:PDF
GTID:2381330590458305Subject:Optical Engineering
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Low-dimensional nanomaterials and structures have potential applications in future photonics chips due to their unique properties.Therefore,it is one of the most important contents to characterize the physical morphology and chemical properties of low-dimensional nanomaterials and structures.The nonlinear information of materials can be obtained by the interaction of ultrafast laser with matter,which is of great significance for studying the nonlinear optical effects of materials.Therefore,in this paper,we built an ultrafast nonlinear spectroscopy and imaging system for the nonlinear characterization of the low-dimensional nanomaterials and structures.The innovation of the research work are as follows: Firstly,based on the tunable excitation source,multi-modal nonlinear spectroscopy and imaging characterization of various low-dimensional nanomaterials and structures can be performed,involving the nonlinear processes such as second harmonic generation(SHG),sum frequency(SFG),four-wave mixing(FWM),two-photon fluorescence(TPF),coherent anti-stokes Raman scattering(CARS)and so on.What's more,the optical system can be flexibly extended the functionality and has the spectral detection capability of time-resolved function.Secondly,based on polarized SHG(p-SHG)effect,for the first time,the femtosecond laser-directed assembly of aligned Zinc oxide(ZnO)nanowire was characterized rapidly,in-situ and non-destructively by using the constructed ultrafast nonlinear spectroscopy and imaging system.The main research contents of the thesis are as follows:(1)Through the theoretical analysis and simulation of the coherent anti-Stokes Raman scattering signal,we had a deeper understanding of the third-order nonlinear process of light-matter interaction,which had certain guidance for the construction of the later optical system.At low numerical apertures,the third-order nonlinear imaging was found to have higher resolution than ordinary linear optical imaging through the simulation process,and the larger the numerical aperture,the higher the resolution of the resulting signal.In the case of high numerical aperture,when the spherical sample size was small(less than 400 nm),the forward and backward CARS signals strength of the spherical sample were similar,and the backward detection was more advantageous for some solvent interference;When the size was large,the backward CARS signal strength is at least two orders of magnitude smaller than the forward direction,which implied that the forward detection method was better.(Chapter Two)(2)Through the guidance of the simulation process,the ultrafast nonlinear spectrum and imaging system were built and applied by the experimental configuration of the collinear CARS and the backward detection method.By adjusting the mirror to realize the spatial coincidence of the two pulse focal points,and time synchronization of two pulse was realized by the generation of the sum frequency signal.Finally the polystyrene beads were used for testing the optical path system,and the CARS spectrum and image detection of the beads were realized.(Chapter Three).(3)The ultrafast nonlinear optical path system was used to characterize two-dimensional nanomaterials and photoresist micro/nanostructures.Firstly,the nonlinear interaction between light and tungsten disulfide material was used to detect the nonlinear spectral information of two-dimensional nanomaterial,which implied that ultrafast laser could excite the SHG,SFG and FWM spectrum of tungsten disulfide material and realize its multimodal nonlinear spectral imaging.Furthermore,we perform FWM imaging of the heterojunction structure,which showed that the layer information of the material can be well characterized.Secondly,the step-type photoresist micro/nanostructure was prepared by two-photon polymerization(TPP).TPF and CARS imaging technology have been successfully used to characterize the quality and layer number information of the prepared micro/nanostructure,in which the CARS imaging had a higher contrast ratio than TPF.(Chapter Four)(4)There currently lacks an in-situ,rapid and effective visualization tool for characterizing the distribution and orientated placement of as-doped nanowires in the composite resins.Herein,we developed an in situ,rapid and non-destructive p-SHG imaging method to characterize the femtosecond laser-directed assembly of aligned ZnO nanowires.We prepared the ZnO nanowire-doped micro/nanostructures by TPP and theoretically analyzed the relationship between the intensity of p-SHG signal and the arrangement direction of ZnO nanowires.The directional arrangement of doped ZnO nanowires resin was in first time successfully characterized by p-SHG optical microscopy.The intensity of SHG signal is correlated to the angle between the laser polarization and nanowires.The p-SHG method will have great application prospects in the characterization of micro-nano functional structures and device fabrication.(Chapter Five)...
Keywords/Search Tags:Ultrafast laser, Nonlinear optics, CARS simulation, Two-photon polymerization, Polarized second harmonic generation
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