The Study Of Electro-optical Modulator Based On Surface Plasmons And The Evanescent Field-excited Surface Plasmon-enhanced Raman Scattering

Since 1960 s the concept of surface plasmons(SPs)is put forward formally by the American-born theoretical physicist,R.H.Ritchie,the electronic collective resonance occurring at the interface between metal and dielectric has been attracting the scientists all of the world.As the evanescent field spreading in the interface,SPs is sensitive to the refractive index of the medium in sub-micron scale and quickly applied in the field of biological interfacial sensing.Until now surface plasmon resonance(SPR)sensor is still one of the widely used methods for effective biological sensing.From the beginning of the 21 st century,as nanotechnology grows rapidly,the amazing feature of SPs that can limit light electromagnetic field breaking through the diffraction limit were found and was quickly applied in the field of nano photonics to develop the micro-nano scale devices.Nowadays despite various micronano-scale electro-optic modulator is reported,SP devices able to modulate effectively the light propagation are still in great demand.In contrast,the link between SPs and SERS is earlier,even in the 1970 s when SERS phenomenon was reported firstly.SPs and SERS are complementary to each other,because SPs contributes the most important part of SERS enhancement and SERS is also the most attractive application field of SPs.The basic interface optical behavior of SPs is the kernel of this Ph D research.After years of research,the coupling mechanism of SPs in the micro scale has become the key to design photonics device and SERS.In this paper,the research was based on this point.The main research contents have the following threeaspects:1.An active-controlled plasmonic device is designed and fabricated based on the index-sensitive property of the SPs.We utilize a one-dimension silver nanograting with a period of 320 nm overlayered with a liquid crystal(LC)layer(50 ?m in thickness),to selectively transmit the surface plasmon resonance(SPR)wavelength.This device realizes the active,reversible and continuous control of the transmitted light via modulating the external voltage signal applied on LC layer.This voltage-controlled plasmonic filter has the dynamic wavelength modulation range of 17 nm,the fast respond speed of 4.24 ms and the low driving voltage of 1.06 V/mm.This study opens up a unique way for the design of tunable nanophotonic devices,such as a micro light source and a switch.More details in Chapter 2.2.To achieve in site characterization with surface-enhanced Raman spectroscopy(SERS)much attempt has focused to optimizing the structure and material with the guiding of three fundamental challenges of SERS,namely sensitivity,repeatability and reliability.However it is rarely concerned to match the optical system and SERS substrate.Here the strategy named integrated plasmon-enhanced Raman spectrograph(i PERS)is presented to effectively integrate SERS substrate with Raman spectrograph.A nanoparticle-on-film system is adopted in i PERS because of its huge electromagnetic field enhancement in near field and directional SERS emission in far field.An aplanatic solid immersion lens is built to directionally excite and collect the SERS signal.The SERS spectra detected by i PERS from the monolayer of para-Aminothiophenol molecule assembled in the nanogap between the nanoparticle and film reveals the ability to monitor plasmonic photo catalysis reaction in nanoscale,indicating the bright future for the monitor of interfacial reactions.More details in Chapter 3.3.The localized surface plasmons(LSPs)around nanoparticles play the central role in SERS detection.In the past decades,the size,morphology,and the aggregation are discussed.However the electromagnetic(EM)field to excite the LSPs is rarelyconcerned.Here the waveguide based evanescent field(WEF)is adopted to excite the LSPs on the hexagonal close-packed Ag nanodot array.Compared with the directly excitation,the intensity of the electric field will be further improved almost to 1 order of magnitude(2 to 4 order of magnitude in SERS)when excited by the WEF.In addition,the EM distribution of the LSPs excited by the WEF depends on the incident polarization.The position of the hot spot can be tuned flexibly at different positions on the NPs.This technique provides us a unique way to further improve SERS intensity on the substrates such as novel metal nanoparticles,SHINNERS and even TERS.More details in Chapter 4.