One of many possible applications of a one-dimensional photonic crystal (1DPhC) is sensing utilizing the Bloch surface wave (BSW). In this paper, we present a method of relative humidity (RH) sensing based on the phase shift of the BSW supported by a truncated 1DPhC represented by a multilayered structure. The structure is composed of six TiO2/SiO2 bilayers with a termination layer of TiO2. The BSW is excited by a total internal reflection of light in the Kretschmann configuration. A spectral interferometric technique is used to obtain a channeled spectrum due to projections of both reflected s and p polarized light waves. The phase is retrieved using a Windowed Fourier transform and spectral derivatives forming peaks are calculated. The sensing concept is based on tracking the derivative peak as a function of RH. A sensitivity to humidity of 0.028 nm/%RH and figure of merit of 0.0042 %RH−1 were determined.
A phase detection method is proposed and demonstrated to measure the response of surface plasmon resonance (SPR) in the spatial domain. In an experimental setup comprising a laser source, a launching optics, a gold coated SF10 glass plate, a coupling prism, a Wollaston prism and a CCD camera, a spatial interference fringes are recorded. Two such spatial interferograms, one including interference of p- and s-polarized waves from the SPR structure for air when the SPR phenomenon does not occur, and the other one for an analyte when the SPR phenomenon occurs, are used to detect the SPR phase shift at the source wavelength. The interferometry setup is used to measure the SPR phase shift for aqueous solutions of ethanol. The measurements are accompanied by theoretical modeling of the SPR responses using the material characteristics, that is, the refractive index of the SF10 glass, the complex refractive index of gold, and the refractive index of the analyte.
In sensing applications utilizing the effect of surface plasmon resonance (SPR), a thin film of gold is widely used as the plasmonic layer. Despite advantages of gold over other metals, characterization of its optical properties is not sufficient as is evident from the measured responses at different angles of incidence. In this paper, a new method of determining the optical constants of a thin golden layer is presented. The method is based on measuring the phase shift between p- and s- polarized optical waves induced by SPR for air in the Kretschmann configuration with an SF10 glass prism and an SPR structure. The SPR structure comprises a gold coated SF10 slide with a chromium adhesion layer. In addition, a birefringent crystal is included in the setup to attain the spectral interference. Information about the phase shift induced by SPR is inscribed in the spectral interferogram recorded by a spectrometer and can be retrieved using the Fourier transform analysis. The measurements are performed for different angles of incidence to obtain the spectral dependence of the optical constants of the golden layer. Measured data are fitted to a model and in addition, the feasibility of the method is demonstrated in measuring the phase response for distilled water.
A new method of sensing small refractive index changes of a liquid analyte using the effect of surface plasmon resonance (SPR) at different angles of incidence is presented. The method is based on detection of the phase shift induced by SPR in the Kretschmann configuration with an SPR structure comprising an SF10 glass prism, a gold coated SF10 slide with chromium adhesion layer, and an analyte (aqueous solutions of ethanol). First, the theoretical modeling of the phase shift at different angles of incidence induced by SPR is performed using the material dispersion characteristics. The phase shift at different angles of incidence is evaluated at a specific wavelength as a function of the analyte parameter and sensitivity is specified. Second, the theoretical modeling is accompanied by an experiment utilizing a polarimetry setup to detect the spectral phase shift induced by SPR. In addition, the phase shift is measured at a specific wavelength as a function of the analyte parameter, and the sensitivity is determined for different angles of incidence.
A spectral interferometric technique to detect the phase shift induced by surface plasmon resonance (SPR) in the Kretschmann configuration is used in sensing small refractive index changes in a liquid analyte. The technique employs a polarimetry setup with an SPR structure comprising an SF10 glass prism, an immersion oil and a gold coated SF10 slide with a adhesion layer of chromium. In this setup two channeled spectra are recorded to detect the spectral phase shift induced by SPR. One spectrum includes reflection of p- and s- polarized waves from the SPR structure for air when the SPR phenomenon does not occur in the source spectral range, and the other one is for an analyte when the SPR phenomenon occurs. The polarimetry setup is employed to measure the spectral phase shift for aqueous solutions of ethanol. In addition, the phase shift is measured at a specific wavelength as a function of the analyte parameter, and the sensitivity is determined. The measurements are accompanied by theoretical modeling of the phase shift induced by SPR using the material dispersion characteristics, i.e., the refractive index dispersions of the SF10 glass, gold, and the analyte.
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