Polarization property associated with surface plasmon resonance in a metal grating in a conical mounting and its application to refractive index sensing

Abstract

We focus on the normalized Stokes parameter s 3 of the specularly reflected light from a metal grating in a conical mounting in order to accurately and sensitively detect the occurrence of surface plasmon resonance (SPR). Experimental and theoretical investigations into the incident angle dependence of s 3 reveal a rapid change in s 3 around the resonance angle θ s p at which SPR occurs. The rapid change in s 3 has features that are successfully applied to SPR sensing: the zero-crossing point of s 3 determines θ s p , and s 3 in the vicinity of θ s p varies markedly in response to a small change in the refractive index of a sample. An experiment using gas samples demonstrates that SPR sensing that considers the rapid change in s 3 clearly detects a refractive index change on the order of 10 − 5 .

Polarization Property Associated with Surface Plasmon Resonance in a Palladium Thin-Film Coated Aluminum Grating in a Conical Mounting and Its Application to Hydrogen Gas Detection

“…The curve shows the partial absorption of the incidental light as a dip in the vicinity of and rapidly fluctuates between a positive maximum value and a negative minimum value via zero at . The rapid change in as well as the absorption dip of is caused by the occurrence of SPR [ 23 ]. The SPR of in the bare Al portion is associated with the coupling of the TM component in the −1st-order evanescent mode with the surface plasmon wave propagating along the surface of the aluminum grating [ 33 ].…”

“…We examined a metal diffraction grating coated with a Pd thin-film which served as a coupler to excite surface plasmons and a transducer to convert hydrogen exposure to a change in its complex refractive index. We have observed that UV holographic aluminum gratings from Edmund Optics, Inc., Tokyo, Japan which have a shallow groove depth of several tens of nanometers, exhibit sharp SPR characteristics [ 23 , 26 ]. In this study, we used a UV holographic aluminum grating, with a groove density of 2400 lines/mm (Edmund Optics, Inc., stock no.…”

“…SPR in a metal grating, in a conical mounting, has been studied [ 27 , 28 , 29 , 30 , 31 , 32 ], and it has interesting features for refractive index sensing [ 25 , 28 , 31 , 32 ]. In particular, the polarization property of the reflected light associated with SPR is attractive [ 23 ]. When the TM-polarized light is incidental on either the Pd-deposited portion or the bare Al portion on the aluminum grating in the conical mounting, TM and TE components appear in the diffracted light.…”

“…Thus, SPR occurring in the Pd thin-film coated aluminum grating includes the information of a small change in the complex refractive index of the Pd thin-film layer due to hydrogen gas exposure. To accurately and efficiently detect the complex refractive index change in the Pd thin film layer, we applied an SPR sensing technique that uses a polarization property of (specularly) light reflected from a metal grating [ 23 ]. Regarding this sensing technique, a metal grating is arranged in a conical mounting, where the plane of incidence is not perpendicular to its grooves [ 24 , 25 ]; then, the normalized Stokes parameter, , of the reflected light (which means that the intensity difference between the right- and left-circularly polarized components) is measured.…”

“…The rapid change in results in the following interesting features of refractive index sensing: is determined as the zero-crossing point on the curve (incident angle dependence of ), and a small change in the refractive index of a sample is detected by measuring under the fixed angle of incidence, which is . The effectiveness of the SPR sensing technique, using the rapid change in has been demonstrated by experiments comprising the following: detection of the refractive index difference among gaseous samples, including H 2 , O 2 , N 2 , and CO 2 [ 23 ], and ethanol concentration measurements of ethanol–water solutions [ 26 ]. In these experiments, the variations in a real refractive index were detected using an aluminum grating in a conical mounting.…”