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Design And Application On The EF-SERS Optic Fiber Sensor

Posted on:2005-10-12Degree:MasterType:Thesis
Country:ChinaCandidate:L ChenFull Text:PDF
GTID:2168360125950254Subject:Electromagnetic theory and microwave technology
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As we all known, there is evanescent field when the light takes internal total reflection on the interface of the rare medium and the denser medium. In this thesis, we designed a Optical Chemical Sensor based on the evanescent field (EF) in the optical fiber.Surface-enhanced Raman scattering (SERS) has long been a matter of great concerns since its discovery in 1974. As a powerful spectroscopy analysis tool, SERS has many excellences over other analysis tools, though scientists have not understood its essential mechanism completely. SERS has been applied extensively in various important fields (molecule surface absorption, biochemistry, corrosion-proof of metal, high polymer materials, thermal breakdown and catalysis, trace analysis, photo conducting device and LB film, etc.).The sophisticated technologies on fiber optic manufacture and application have also been developed in recent years. All these put the foundation to the development of SERS optic fiber sensor. The combination of the optic fiber and the technology of the SERS spectroscopy, one of the evolvements to Optical Chemical Sensor (OCS).In this thesis we used the EF as exciting field, thus the surface plasma resonance between the evanescent wave and the surface plasma produced on the metal film can induced the enhanced field under the function of the evanescent field. In fact, belonging to the OCS, the EF-SERS fiber sensor is one of the important branches of SERS spectroscopy. OCS, expressing the chemical information from the analytes by optical properties such as, absorption, reflection, fluorescence or chemical luminescence, scattering, refraction and polarization, are transduced setups that are based on the spectroscopy chemistry and optics waveguide and the technique of measurement the EF-SERS optic fiber sensor has many advantages. For example, giving more information on the molecular structure, reducing the effect of background, providing remote sensing to the harmful environment, in situ monitoring the reaction process for the kinetic mechanism, also in situ monitoring some danger process. It can be used as the complemental sensor to other sensors at the same time.The thesis consists of the following contents:We calculated the enhanced factor of the local field by SPR between the surface plasma wave and the evanescent wave in the EF-SERS fiber sensor. The dielectric function of some metals at optic band is analyzed. The result of calculation demonstrates that Ag is the best metal for surface enhanced Raman scattering. On roughed Ag surface, Raman spectrum can be increased by six orders of magnitude, when surface plasma resonance (SPR) is excited. Analysis also demonstrate that some factors effect the SPR very much.The calculation showed that the factor was related to the following parametera,The dielectric constant out of metal particleWhile the dielectric constant out of the metal particle increase, the frequency of SPR shift to low frequency (LF). And the enhancement of located EM field also increases.b,The shape of the metal particleIf the Ag particle is ellipsoidal, the frequency of SPR will shift to LF while the ratio of major axis to minor axis increases.c,The size of the metal particleOn sphere condition, the variety of enhancement is up first, then down.2,The design and the crafts of the EF-SERS fiber sensor optic fiber sensorThe EF-SERS fiber sensor were designed and studied. The fabrication craft concludes cutting, polishing, washing, embellishing and reservation. The key process is embellishing, so the optimized condition is researched. The method through Ag colloid is easier and simplier than that of Ag island film. The assembly of silver colloid particles onto the fiber by N-metal bond formed a homogeneous and stable film. Self-assembled Ag colloid film had both the optical properties of colloidal particles and the convenience of the solid substrate after absorbed onto the fiber tip. It preserved the aggregation at some degree while avoiding being subject to aggregating to deposit and the unstab...
Keywords/Search Tags:Application
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