Research On Film System For Surface Plasmon Excitation

Surface plasmon polaritons?SPPs?is an electromagnetic mode generated by the interaction between free electrons exsiting on the metal surface and photons.The sensing technique based on surface plasmon resonance?SPR?has been rapidly developed owing to its feature of high sensitivity and used in a wide range of applications including biosensing,chemical analysis,drug development,environmental monitoring and medical diagnostics.In this dissertation,the research of films for SPR measurement system is carried out.Several relevant problems which need to be solved are shown as follows:improvement of measurement apparatus for spectral and angular resonance,improvement of algorithm for determinating the dispersion characteristics of films,research of dispersion and sensitivity characteristics of high performance and low cost films,design of prism-based wideband reflective transverse magnetic?TM?polarizing films and application of the polarizing films in SPR.Based on the principle of angular resonance of SPR,a new method of determinating the dielectric constants and thicknesses of films is proposed.The method does not involve complex formats and algorithms,the ambiguity of solution can be eliminated in the calculation process.We improved the proposed method of determinating the dispersion characteristics and thicknesses of films based on the principle of spectral resonance of SPR to make it more reasonable and more versatile.Measurement apparatus for spectral and angular resonance of SPR which can calibrate the absolute value of incident angle is built up.The SPR responses of Au film are measured by using two apparatus,and the dielectric constants and thickness of Au film are determined.A method of extracting angular reflectivity from spectral reflectivity of SPR is presented.According to the characteristics of two apparatus,two apparatus are integrated into one apparatus which can both measure the angular and spectral reflectivity achieving low-cost and multifunctional.The spectral responses and dispersion characteristics of Cu/TiO₂,Ag/TiO₂ films are investigated.The sensitivities of prism-based SPR refractive index sensors using the films are analyzed theoretically utilizing the dispersion characteristics of films.The results show that Cu/TiO₂ films are more suitable for SPR refractive index sensors than Au film because they exhibit higher sensitivities.The sensitivities for both angular and wavelength modulation of Ag/TiO₂ film are close to those of Au film.The sensitivities of Ag/dielectric film can reach the same level of Au film by choosing the parameters of dielectric film suitably.The use of Cu-based and Ag-based films is capable of reducing the cost of SPR chips effectively on the premise of remaining high sensitivity.A prism-based wideband reflective TM polarizing film composed of Cr and SiO₂films is designed.The performances of polarizer consisting of Cr/SiO₂film and K9prism are analyzed theoretically.The polarizer can sufficiently reflect TM-polarized light and severely absorb TE-polarized light in a wavelength range from 600 nm to 900nm.By suitably choosing the film thicknesses,the operation angles of such polarizers can be adjusted over a wide angle range greater than the critical angle of total reflection.Such polarizers are compitable with Kretchmann SPR configuration which is particularly convenient for integrating polarizer with coupling prism.Based on the principle of Coupled Plasmon-Waveguide Resonance?CPWR?,a prism-based wideband reflective TM polarizing film composed of Ag,Cr and TiO₂films is designed and fabricated.The spectral responses of polarizer consisting of Ag/Cr/TiO₂ film and K9 prism are investigated experimentally using the apparatus for measureing spectral reflectivity of SPR.The operation angles and wavelength of polarizer range from about 42°to 47°and 600 nm to 900 nm,respectively.In the wavelength range,TE lights are severely attenuated,while TM lights remain relative high reflectivity.The experimental results agree closely with simulation.We presented a Kretchmann SPR configuration for wavelength modulation with an integrated polarizer by combining polarizer with Au film.The configuration exhibits good SPR spectral responses,the feasibility of integrated Kretchmann SPR configuration is demonstrated experimentally.Such polarizing films can simplify SPR apparatus and reducesthe cost providing a new approach to realizing integrated SPR configurations.