Fundamental Research And Application Of A Novel Scanning Near-field Optical Microscopy

Near-field scanning optical Microscopy?NSOM?with rapidly developing is becoming an irreplaceable tool for nanoscale characterization,whose application value is increasingly prominent.It is approached by a near field probe which can couple the undetectable evanescent wave into far field signals such as scattering light that is detectable and hence breaks the diffraction limit.Due to the advantages of super-resolution,label-free,multi-parameters,it is widely used in many fields,such as physics,chemistry and biology.However,traditional near-field scanning microscopy has limited resolution,complicated processes and is time consuming owing to the probe.In recent years,near-field scanning optical imaging is reaching for higher resolution,faster imaging speed,more optical parameters characterization and conventional imaging conditions,along which new types of probes are developed.But,still,it suffers few parameters that is able to detect and difficulties to extract signals,etc.The main content includes:1.Electric filed imaging of focused vector beam,including selectively imaging for either longitudinal or transversal components.Metal nanoparticle on metal film is designed as a probe for imaging of the longitudinal component,of which the mechanism of the polarization response is studied theoretically.In experiment,silver nanoparticle on silver film is selected to characterize longitudinal component of several different types of tightly focused beam,which shows a feasibility and superiority.While for imaging of the transversal component,dielectric nanoparticle on metal film is chosen as a probe of which the polarization response is also studied.Combining theoretical and experimental results the optimized size of dielectric nanoparticle is selected.The intensity distribution of the transverse field component of the common surface plasmon polariton?SPP?light field is then imaged.The study of this section solved the key problems of traditional NSOM with single imaging parameter,difficult signal extraction and low imaging efficiency.2.Spin characteristics study of focused vector beam,including transverse spin of tightly focused vector field and longitudinal spin of SPOV field?SPP with optical vortex?.For the transverse spin of the tightly focused vector light field,a qualitative study is made through surface plasmon emission?SPCE?.For the longitudinal spin of SPOV field,a fine longitudinal spin structure of SPOV based on the local spin of optical field is presented.The spin structure is characterized by experiment,and the result is15nm.In addition,a fine spin structure of conjugated SPOV field is designed for ultra-high precision position detection.The accuracy in experiment is about 1nm,the detection range is¹00 nm,and the ratio of accuracy to is 10^-5.This accuracy is the highest level in the research of position detection by optical means which is expected to be applied in high-precision nano-positioning platform,AFM feedback system and other high-precision location requirements.This section breaks through the difficulty to experimentally research on the spin characteristics of tightly focused vector field.Meanwhile,an application scenario is presented,which shows the advantages of spin characteristics to the level of practical value.3.Polarization-controlled gap-mode surface enhanced Raman scattering?SERS?.Both theory and experiment studies are involved and the results prove that the polarization of incident light influences the enhancement of SERS.It reveals that the coupling ability of the gap structure with radially polarized light is much better than conventional linear polarized light.Further,modulating radially polarized light is presented to generate perfect radially polarized light,which is applied to the Raman detection based on the gap structure of metal nanoparticle and metal film.Higher SERS enhancement ability is achieved,more than 20 times,compared with ordinary radially polarized.This research leads a new way that one can get further SERS enhancement by modulating the excitation light,which is simpler and more effective than by improving the substrate.