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Research On Refractive Index Measurement System Based On SPR Using Wavelength Modulation

Posted on:2013-01-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y HuangFull Text:PDF
GTID:1118330374454304Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Surface plasmon resonance (SPR) phenomenon exhibits extremely high sensitivityto the refractive index of the surface layers above the SPs-supporting metal films.Owing to this feature, SPR sensing technique attracts considerable attention, and hasbeen rapidly developed and used in a wide range of applications including biosensing,chemical analysis, drug development, food safety, environmental monitoring, medicaldiagnostics. Based on modulation approachs, SPR sensors can be classified as SPRsensors with angular, wavelength, intensity and phase modulation. In this paper, theresearch of SPR sensing technique based on wavelength modulation is carried out, inorder to solve several key problems, including precise determination of dispersionproperties of thin metal films, mutual restriction of measuring range and sensitivity/resolution in measuring refractive index, fast analysis of wavelength sensitive propertiesof gas sensitive films, and so on.Determination of thicknesses and optical dispersion properties of thin metal filmsby using SPR wavelength modulation approach. Determination of complex refractiveindex and thickness correctly is very important to SPR sensing technique, due to twomain reasons: thin metal films are an integral part of the SPR sensors, and theperformance of these sensors is dominantly determined by the optical constants andthicknesses of the metal films; parameters of the overlayer deposited above the metalfilms are often required to be determined correctly, and it is evident that the metal filmsmust first be characterized precisely. Wavelength modulation SPR sensor requires theoptical constants of thin metal films in a wavelength range, i.e., the dispersionproperties of thin metal films. At present, optical constants of thin metal films at a singlewavelength or several wavelengths have been studied using SPR technique with angular modulation approach. But using angular modulation approach to study the dispersionproperties is intrinsically complex, because the measurement of optical constants mustbe performed repeatedly at a series of sampled wavelengths. In this paper, we proposeto use wavelength modulation approach, i.e., the spectroscopy of surface plasmon infrequency domain to characterize the dispersion properties and thicknesses of thin metalfilms. Using broadband light source (tungsten halogen lamp) with a single scan of theincident angle, a series of dielectric constants over a wide spectral range can bedetermined simultaneously, and the dispersion curves can be obtained.Research on measurement system of refractive index based on wavelength andangular combined SPR modulations. To wavelength modulation SPR sensor, themeasuring sensitivity of refractive index increases with wavelength. A broadband lightsource (700nm~900nm) with relative narrow bandwidth at long wavelength is selected,to measure the refractive index of surrounding medium by using SPR reflection powerspectrums, in order to obtain relatively higher sensitivity and resolution. But themeasuring range of refractive index is decreased by the reduction in bandwidth of lightsource. In order to solve the mutual restriction of measuring range and sensitivity/resolution, sectional measurement method is adopted, i.e., different incident angles areselected respectively, which will detect different measuring ranges of refractive index.Wavelength and angular combined SPR modulations can cover the whole measuringrange of refractive index, and improve the measuring sensitivity and resolutionsimultaneously.Analysis of wavelength sensitive properties of gas sensitive films by using thespectroscopy of surface plasmon in frequency domain. Take sensitive films of ethanolgas (three layer films system of Cr-Au-TiO2) for example, the relationship betweenwavelength and refractive index can be obtained precisely and conveniently, by usingthe spectroscopy of surface plasmon in frequency domain, furthermore the wavelengthsensitive properties of sensitive films will be given. This analysis method provides effective experimental means for designing, optimizing and preparing the sensitivefilms.
Keywords/Search Tags:Surface Plasmon Resonance (SPR), Dispersion property of thin metal film, Sensor, Wavelength modulation, Refractive index measurement
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