Study On The Property Of Super-resolution And Super-absorption Of Metamaterials-based Micro/Nanostructures

Surface plasmons(SPs)are surface electromagnetic waves trapped at the metal-dielectric interface due to the collective oscillations of free electrons of the metal.Their intriguing properties such as strong localization and large in-plane momentum nature have been exploited for applications in biosensors,nonlinear optics,super-resolution imaging and perfect absorbers.Metamaterials are unnatural materials composed of metallic/dielectric micro/nanostructures and they have recently attracted increasing attentions.Due to the surface plasmons resonant,metamaterials have many exotic optical properties in electromagnetic responses.However,the wave vector in micro/nano metamaterials is not very high and the bandwidth of absorption of metamaterials is not broad at present.Therefore,they could not meet the requirement on the optical super-resolution and ultra-broad absorption in the visible domain.In view of above mentioned problems,this thesis mainly focuses on the super-resolution optical imaging and the perfect absorbers of metamaterials.The contents and achievements of this study are presented as follows.1.Study on the super-resolution optical imaging.(1)A gradient permittivity metamaterial structure(GPMS)is designed.This kind of structure consists of three successive dielectric films of decreased gradient permittivity with thin silver films in between dielectric films.By employing finite-difference time domain(FDTD)method,the proposed GPMS is carefully simulated and analyzed,and it is found that the standing SPs wave with an 84 nm period in one dimension can be obtained for a 532 nm incident wavelength.In addition,the possibility to improve the imaging resolution by employing the GPMS in the plasmonic structure illumination microscopic(PSIM)method is demonstrated theoretically.It is found that a resolution less than 45 nm can be achieved in one dimension in GPMS which is a 5.6-fold improvement as compared with that of the conventional epifluorescence microscopy.(2)Based on above work,we propose a meta-sandwich structure(MSS).It is found that the minimum period of the plasmonic interference pattern obtained is 31 nm for a 532 nm illumination wavelength.As a result,a resolution of 16 nm can be achieved in one dimension in PSIM by employing the proposed MSS structure as the illumination source in plasmonic-based microscopy.The validity of the MSS in supporting short wavelength SPs wave is proved by employing both rigorous numerical and analytical methods.(3)A dynamic wide-field optical nanoimaging method based on a meta-nanocavity platform(MNCP)model incorporated in micro/nano-fluidic systems is proposed.The samples to be observed can be confined in nano-scale space for the ease of imaging.It is found that this platform can support standing wave surface plasmons(SW-SPs)interference pattern with a period of 105 nm for 532 nm incident wavelength.Furthermore,the potential application of the MNCP for wide-field super-resolution imaging is discussed and the simulation results show that an imaging resolution of 60 nm can be achieved.The effectiveness of the MNCP in fluorescent imaging and the imaging results of this MNCP applied in PSIM are also discussed.2.Study on the super-absorption.(1)An efficient terahertz multiband metamaterial absorber is designed,which over 91% absorption at four targeted resonant frequencies can be achieved.And these frequencies are close to the absorption spectra of four drugs from 1.4 to 2.7 THz.The high absorptivity of the proposed absorber can be explained by the synergistic effect of the localized surface plasmon resonance enhancement,the Fabry-Perot resonant and the slow light effect.The error analyses of different structural parameters show that the error of the gap between subunits has a great effect on the absorbing performance but the radius of the vertex of the microfan has nearly no effect.(2)A light absorbing model based on the hierarchic structure with randomly distributed nanospheres is proposed,which over 90% absorption over 400-900 nm can be achieved.In comparison to the structure of the traditional sandwich-like absorber,the random sphere model shows a great enhancement effect on the light absorption.The high absorptivity can be explained in terms of the localized surface plasmon resonance effect and the strong scattering of Au NSs embedded in the TiO2 medium.Finally,the effects of different parameters of random nanospheres on the light absorption were also analyzed and discussed.It is found that the large range of radius distribution and the large numbers of nanospheres(i.e.dense nanospheres),are not preferable for the light absorbing.