Metal-dielectric Waveguide Based Near-field Characterization And Wide-field Super-resolution Microscopy

Super-resolution microscopy plays an important role in nano-optics and life science,and is the most important research field in optics.At present,various kinds of super-resolution microscopies have their own merits.Among them,structured illumination microscopy（Structured illumination microscopy,SIM）is a fast and wide-field super-resolution microscopy with loose requirement for fluorescent dyes,but its resolution enhancement is limited.However,the resolution and the signal-to-noise ratio can be improved by combining total internal reflection（Total internal reflection fluorescence,TIRF）or surface plasmon polaritons（SPPs）with SIM configuration,termed as TIRF-SIM and PSIM.PSIM has a strong field enhancement effect due to the resonance nature of SPP.In practice,nevertheless,metal substrates are often destructive to biological cells,such as rejection and non-adherence.Moreover,biological tissue exists in the water environment,where SPPs often show a strong Ohmic loss.These problems limit its application in bio-imaging.In order to solve the above problems,this paper mainly makes the following efforts:1.A metal-dielectric waveguide（MDW）is proposed to reduce the Ohmic loss of traditional SPPs.By adding a dielectric layer,most of the energy at metal/water interface is transferred to the dielectric/water interface,thus greatly reducing the loss of evanescent waves.With this structure,the propagation distance of evanescent waves in water environment is increased by about one order of magnitude.To further improve the spatial resolution,an MDW structure based on aluminium film is proposed for shorter wavelength（blue light）.The low-loss evanescent waves at dielectric/water interface is obtained.Furthermore,the wavelength of evanescent wave can be modified within a certain range by adjusting the structure.2.A method for characterizing the electromagnetic near-field components based on MDW structure has been developed.Firstly,the longitudinal electric near-field components generated by the first two MDW structures were characterized by using metal nano-particles as near-field probes.Then,the near-field longitudinal magnetic components of TE mode in MDW structure were successfully characterized by using high-refractive-index particles,due to the directional radiation.3.Based on the previous work,we propose a wide-field super-resolution microscopy,termed as MDW-SIM.Due to the low-loss and resonance nature of MDW mode,surface field enhancement larger than TIRF-SIM can be achieved.The introduction of dielectric layer reduces the quenching and avoids the harmful effects on biological samples arised from metal film,which are the disadvantages of PSIM technique.From the bright ring of SPCE,it can be seen that the initial wave vector of fluorescence signal is larger than that of the total reflection angle of TIRF,which should be one of the factors to improve the imaging resolution,due to the MDW structure.The fluorescent beads with nominal diameter of 40nm were imaged by an objective with numerical aperture of 1.45 when incident wavelength of 473nm.The full width at half maximum of the fluorescent bead reached～86nm（0.18λ₀）,and two adjacent beads with～102nm separation can successfully be distinguished.Finally,fibroblasts were also imaged by the proposed system.