Researches And Applications Of Angle-resolved Spectroscopy Of Raman And Fluorescence Based On Surface Plasmons

Plasmonics have been received much attentions due to their excellent ability tocontrol light in subwavelength range. Surface plasmons (SPs), which could be as thebridge to link the far field and near filed of light, could control light beyond thediffraction limit. Therefore SPs have wide applications in the development andpreparation of the nano-sized optical elements. SPs are also important to surfaceenhanced spectroscopy, such as surface enhanced Raman (SERS) and surfacePlasmon controlled fluorescence. Due to the SPs resonance effect, the localelectric-magnetic fields could be effectively enhanced, thus the spectrum signals (e.g.Raman scattering) could be improved for several orders. Besides, the coupling of SPsand light wave is usually directional, thus the emission direction of light could betuned by SPs. In this work, we studied some issues about the directional spectroscopyby means the self-built angle-resolved spectrometer:1.We studied the directional emission of SERS. The SERS enhancement factorcould reach109-1010according the electric-magnetic (EM) enhancement mechanismof SERS. It is not strong enough to detect the SERS signal of single molecule (>1014).To achieve the single molecule SERS, other enhance approach should be employedsuch as the resonance enhancement and charge transfer effect. However thesechemical enhancement methods which strongly depend on the species of themolecules are not universial methods. Thus any way to provide extra enhancement issignificant to SERS. The collection efficiency of SERS is usually very low due to theemanative nature of scattering. The SERS sensitivity could be efficiently improved ifthe SERS collection efficiency is improved. We studied the propagating SPs couplingemission on kretschmann configuration and periodical nano-well array. The directional SERS was achieved. Even the emission direction of SERS could along thenormal line of substrate after optimizing the parameters of the structure. We believe itis beneficial to improve the collection efficiency of SERS. The details could be foundin chapter2.2.We developed some Raman detection platform to match some special detectionrequirements. The commercial device could match the most detection requirements,however some special samples could not be detected, therefore the development ofnew detection devices is very important to improve the quality of the scientificresearch.1. We developed several novel Raman spectrometers based our previousresearch results: we developed a portable SERS spectrometer based on the directionalSERS phenomenon. The SERS spectrometer has a high sensitivity and accessibility;2.We built a compact microfluidics Raman spectrometer which is convenient to detectRaman on chips to solve the problem that the traditional Raman spectrometer is notsuitable to detect Raman spectra on microfluidic chips,;3. We integrated fluorescenceimage and dark field image with Raman spectrometer. We can fast locate theinterested samples of transparent biological samples or nanoparticles usingfluorescence image and dark field image, and then analyzed the components of thesample by Raman spectra. These self-built detection platforms has more flexiblefunctions comparing the commercial instruments, which is the hardware basics toresearch the challenging projects in our research group. The details could be found inchapter3.3.The control of light emission directions using electric signals. Since SPs is verysensitivity to the refractive index (RI) of surrounding, and the RI of liquid crystalscould be tuned by electric signals, we could tune the plasmonic devices by voltagesignals based on this. We achieved the electric control of the wavelength and emissiondirections of fluorescence on kretschmann configuration and nanograting structure. Itwas proved that the modulation method using liquid crystals was very efficiently. Thedetails could be found in chapter4. In additions, we tuned the light beam transmissiondirections based on SPs induced extraordinary optical emission. A liquid crystals layerwas added on the thick Ag film with nanograting pattern, and the beam transmissiondirections could be tuned. It is a very simple, but very efficiently method to modulate the beam directions. This research achievement could be using in three-dimensionaldisplay fields. The details could be found in chapter5.