Abstract
We present a method for improving the sensing capability of grating coupled surface plasmon resonance (GCSPR) sensors. The grating is rotated azimuthally (phi) until the excitation of double surface plasmon polaritions (SPPs) by a single wavelength is possible. Close to this condition, further tuning of the incident wavelength will merge the double SPPs into a multi-SPP resonance which is angularly broad but spectrally sharp. This is the condition where the momentum vector of the propagating SPP is perpendicular to the incident light momentum. We demonstrate this sensitivity enhancement on a Au grating surface using a dodecanethiol (C12) self-assembled monolayer (SAM). Using this method, a shift in resonance angle as large as 3 degrees can be observed. The simulated sensitivity of this method shows that a sensitivity up to 800 degrees /RIU is achievable, which is one order of magnitude greater than that in a conventional fixed grating (phi = 0 degrees ) as well as the prism-coupled Kretschmann configuration.
Highlights
We present a method for improving the sensing capability of grating coupled surface plasmon resonance (GCSPR) sensors
Surface Plasmon Polaritons (SPP) are electromagnetic waves coupled with surface plasma charge oscillations that propagate along the metal/dielectric interface
The occurrence of double SPP reflectivity dips for a single incident wavelength is due to double matching in the momentum conservation condition, as discussed in our previous publication [25]
Summary
Surface Plasmon Polaritons (SPP) are electromagnetic waves coupled with surface plasma charge oscillations that propagate along the metal/dielectric interface. Due to its nonradiative nature, SPP can be excited by an incident EM-wave illuminating the metal surface (Surface Plasmon Resonance - SPR) only in proper configurations such as prism-coupling and grating-coupling setup [1]. The resonance condition is extremely sensitive to the changes in refractive index on the metal film within a thickness comparable to the vertical extinction length of SPP [2]. Due to these properties, SPR reveals itself as a useful instrument for the study of surface optical properties and it is a highly suitable candidate as a sensor for liquid or gas solutions [3,4,5] and surface chemistry [6]. PCSPR sensors suffer from cumbersome optical alignment [15] and are not amenable to miniaturization and integration [16]
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