Conventional Kretschmann Configuration Research Articles

Creatinine Detection by Surface Plasmon Resonance Sensor Using Layers of Cerium Oxide and Graphene Over Conventional Kretschmann Configuration

Creatinine Detection by Surface Plasmon Resonance Sensor Using Layers of Cerium Oxide and Graphene Over Conventional Kretschmann Configuration

Enhanced detection accuracy and signal-to-noise ratio of surface plasmon resonance based refractive index sensor with the addition of thicker layer of Silicon

The improvement in the sensitivity performance of conventional surface plasmon resonance (SPR) based sensors with the addition of thin layers of various high index dielectrics (e.g. 5 nm–10 nm of Silicon) is well established. This improvement in sensitivity comes at a price of reduced detection accuracy, deteriorated signal-to-noise ratio (SNR) and small value of Figure of Merit (FOM). Sensors with high detection accuracy and SNR find applications in the direct detection of small molecular (few hundreds of Daltons) interactions or low molecular concentrations (physiological concentration) on the surface of the sensor. The current paper presents design methodology and theoretical analysis of the performance of SPR based refractive index sensor with enhanced SNR, detection accuracy, and FOM attained when a thicker layer of Silicon (60 nm–400 nm thickness) is introduced in the conventional Kretschmann configuration employing angular interrogation technique. The analysis is valid for any high index dielectric layer that is used to enhance the electromagnetic field associated with the surface plasmon (SP) mode excited at the metal-dielectric interface. In the present paper, we show that the SP mode which participates in the sensing applications can be excited at the metal-dielectric interface for multiple thicknesses of Silicon. Analytical expressions are derived to compute the multiple thicknesses of Silicon using a modal analysis as well as the transfer matrix method (TMM) by considering the SPR sensor as a multi-layered optical waveguide structure. The refractive index SPR sensor with thicker silicon layer is shown to exhibit a long propagation length and large penetration depth in the analyte region, resulting in a higher depth-to-width ratio (defined as the SNR) and detection accuracy in its SPR reflectivity spectrum, hence enhancing the measurement precision of the sensor.

Plasmonic Generation of Spatiotemporal Optical Vortices

We investigate the transformation of spatiotemporal optical signals using the Kretschmann configuration with an additional dielectric layer, which can be referred to as the “generalized Kretschmann setup”. We demonstrate that in the considered structure, it is possible to achieve the condition of generating a reflected optical pulse containing a spatiotemporal optical vortex, which appears to be impossible in the conventional Kretschmann configuration. High-quality generation of spatiotemporal optical vortices using the investigated structure was confirmed by the results of rigorous numerical simulations. The obtained results are promising for applications in analog optical computing and optical information processing systems.

Enhanced SPR-Based Localized and Bulk Sensing Using a Plasmonic Nanopillar Array With Spacer

We report a substantially improved localized and bulk sensing response of a plasmonic sensor based on a plasmonic nanopillar array spacer-separated from a plasmonic thin film and operated using the conventional Kretschmann configuration. This paper describes theoretical investigations of the spectral and angular interrogation of the proposed sensors to determine the spectral or angular reflectivity minima. Shifts in the reflectivity minima are determined to obtain information on perturbations in localized (local binding analyte layer sensing) and bulk refractive index (bulk medium sensing) on the sensor surface. Optimization of the structural parameters of the proposed sensor yields a highly enhanced sensor performance, with an extremely high sensitivity (9920 nm RIU^−1) and figure of merit (58.2 RIU^−1) for bulk sensing response, as well as extremely high sensitivity (76 nm/nm) and figure of merit (0.5 nm^−1) for localized sensing response upon spectral interrogation of the sensor. The localized surface sensitivity for the proposed sensor, which is evaluated to be 76 nm/nm, is higher than what has been reported till now. The proposed sensors do not require any sophisticated optical set-ups and can be implemented on the optical setups used for the conventional Kretschmann configuration based sensors. The proposed sensor design could easily be fabricated using the state-of-the-art top-down nanofabrication approaches and could be employed for developing highly sensitive biosensing platforms.

Investigation of Plasmonic Detection of Human Respiratory Virus.

The COVID‐19 virus has been recently identified as a new species of virus that can cause severe infections such as pneumonia. The sudden outbreak of this disease is being considered a pandemic. Given all this, it is essential to develop smart biosensors that can detect pathogens with minimum time delay. Surface plasmon resonance (SPR) biosensors make use of refractive index (RI) changes as the sensing parameter. In this work, based on actual data taken from previous experimental works done on plasmonic detection of viruses, a detailed simulation of the SPR scheme that can be used to detect the COVID‐19 virus is performed and the results are extrapolated from earlier schemes to predict some outcomes of this SPR model. The results indicate that the conventional Kretschmann configuration can have a limit of detection (LOD) of 2E‐05 in terms of RI change and an average sensitivity of 122.4 degRIU−1 at a wavelength of 780 nm.

Enhancement of Long-Range Surface Plasmon Excitation, Dynamic Range and Figure of Merit Using a Dielectric Resonant Cavity.

In this paper, we report a theoretical framework on the effect of multiple resonances inside the dielectric cavity of insulator-insulator-metal-insulator (IIMI)-based surface plasmon sensors. It has been very well established that the structure can support both long-range surface plasmon polaritons (LRSPP) and short-range surface plasmon polaritons (SRSPP). We found that the dielectric resonant cavity under certain conditions can be employed as a resonator to enhance the LRSPP properties. These conditions are: (1) the refractive index of the resonant cavity was greater than the refractive index of the sample layer and (2) when light propagated in the resonant cavity and was evanescent in the sample layer. We showed through the analytical calculation using Fresnel equations and rigorous coupled wave theory that the proposed structure with the mentioned conditions can extend the dynamic range of LRSPP excitation and enhance at least five times more plasmon intensity on the surface of the metal compared to the surface plasmon excited by the conventional Kretschmann configuration. It can enhance the dip sensitivity and the dynamic range in refractive index sensing without losing the sharpness of the LRSPP dip. We also showed that the interferometric modes in the cavity can be insensitive to the surface plasmon modes. This allowed a self-referenced surface plasmon resonance structure, in which the interferometric mode measured changes in the sensor structure and the enhanced LRSPP measured changes in the sample channel.

Dispersion engineering with plasmonic nano structures for enhanced surface plasmon resonance sensing

We demonstrate numerically and experimentally the enhancement of Surface Plasmon Resonance (SPR) sensing via dispersion engineering of the plasmonic response using plasmonic nanograting. Following their design and optimization, the plasmonic nanograting structures are fabricated using e-beam lithography and lift-off process and integrated into conventional prism based Kretschmann configuration. The presence of absorptive nanograting near the metal film, provides strong field enhancement with localization and allows to control the dispersion relation which was originally dictated by a conventional SPR structure. This contributes to the enhancement in Q factor which is found to be 3–4 times higher as compared to the conventional Kretschmann configuration. The influence of the incident angle on resonance wavelength is also demonstrated both numerically and experimentally, where, only a negligible wavelength shift is observed with increasing the incident angles for plasmonic nanograting configuration. This surprising feature may be helpful for studying and utilizing light-matter interaction between plasmons and narrow linewidth media (e.g. Rb atom or molecule) having nonlocalities in their susceptibility-momentum relation. Finally, we analyze the role of plasmonic nanograting in enhancing the performance of an SPR sensor. Our results indicate that the integrated SPR-nanograting device shows a great promise as a sensor for various types of analytes.

Metal-dielectric multilayer structure supporting surface plasmons: electromagnetic modelling by the method of single expression

Surface plasmons’ (SPs) excitation in Kretschmann configuration, where the thin metallic layer is substituted by a metal-dielectric multilayer (MDML) structure is analysed numerically. For numerical analysis the method of single expression (MSE) is used. Derivation of MSE equations for analyzing TM polarized wave incident on a multilayer structure is presented. First, for validation, an excitation of SPs in conventional Kretschmann configuration with single silver layer is analysed. Further, four possible combinations of MDML $$\hbox {(silver/SiO}_\mathrm{2})$$ structures of different alternation of outermost layers are analysed on the subject of SPs excitation. It is obtained that MDML structures can support SPs at specific number of layers, when the total thickness of metallic layers in MDML structure is less than the thickness of single metallic layer in conventional Kretschmann configuration. It is found, that specific angles of SPs excitation for MDML structures are greater than that for conventional Kretschmann configuration.

Generation of Multiple Plasmon Resonances in a Nanochannel

In this paper, we investigate the coupling of surface plasmon based on Kretschmann configuration (KC) to localized and delocalized surface plasmon modes supported by metallic nanowire grating (MG) at the oblique incidence. The designed structure consists of MG deposited on a substrate positioned upside down above a conventional KC at a certain distance. Mode coupling and resonant interactions between KC and MG create two new hybrid plasmon modes with narrow bandwidths and unique spectra features, resulting in two obvious dips in the reflection spectrum. Although both dips respond nonlinearly to the refractive index (RI) of the dielectric layer, surprisingly, the sum of two resonance wavelengths has a good linear approximation in a wider RI range. The simultaneous measurement of two resonance dips makes it more attractive as a surface plasmon resonance analysis technology, which is valuable for high-sensitivity optical sensors.

Evanescent field excited plasmonic nano-antenna for improving SERS signal

The purpose of this work is to develop a high-performance surface-enhanced Raman scattering (SERS) substrate with high light harvesting and SERS emitting efficiencies based on the principle of a plasmonic nano-antenna. A prism/Ag nanowell array was designed and constructed based on the Kretschmann configuration. Almost 100% of the incident light can be absorbed at the resonance angle. A strong electromagnetic (EM) field is generated in the near field along the rim and at the center of the nanowells by means of the localized energy of surface plasmons (SPs), resulting in the electric field being enhanced 300 times at the Ag surface. The co-enhancement of localized SPs and propagating SPs was achieved in this substrate. The plasmonic nano-antenna structure can also redirect the SERS, which benefits the SERS collection. The SERS sensitivity on this configuration was improved by about 40 times compared with that on a conventional Kretschmann configuration with a flat Ag film. This SERS substrate design with full consideration on the tuning of the EM field in the near field and SERS space distribution in the far field could give insight into the design of a new generation of SERS substrates.

Infrared surface plasmon resonance in a subwavelength metallic grating under illumination at a large incidence angle

Under the condition of illumination at a large incidence angle, surface plasmon (SP) resonances in the conventional Kretschmann configuration occur in the visible wavelength region. In this paper, we show that a subwavelength metallic binary grating that was specifically designed can induce IR SP resonance (SPR) effectively under the same illumination condition. We analyze the structural controllability of IR SPR by subwavelength metallic binary gratings and propose an optimal design of subwavelength grating structures for IR SPR under illumination at a large incidence angle. A numerical design method combining the rigorous coupled-wave analysis and the genetic algorithm is devised.

Tunable long-range surface plasmon polaritons taking advantage of nonlinear surface waves

We present an improved Kretschmann configuration with nonlinear dielectric as substrate, in which long-range surface plasmon polaritons (SPPs) may appear, the modes and propagation lengths are tunable. We numerically simulated the solutions of SPP modes and their propagations. The results show that the SPP propagation length can range from tens of micrometers to tens of centimeters or even longer. The configuration proposed in this letter makes a breakthrough of the intrinsic restriction in conventional Kretschmann configuration and there exist the continuous steady SPP modes also in the range of k0ε31/2>β>k0ε11/2. It allows for optimization of SPP properties and makes SPP application more flexible in practices.

Surface plasmon resonance via polarization conversion in a weak anisotropic thin film

A columnar structured thin film with weak anisotropy is applied to trigger the electromagnetic wave with forbidden polarization state to excite surface plasmon. The precursory work is done here for the conventional Kretschmann configuration [D. Sarid, Phys. Rev. Lett. 47, 1927 (1981)] by arranging an anisotropic thin film in the configuration as a three-layered system (prism/anisotropic dielectric film/metal film/isotropic thin film/air). It enables both p-polarized and s-polarized incident waves simultaneously to excite surface plasmon.

Determination of thickness and optical constants of thin metal films with an extended ATR spectrum

An extended attenuated total reflection (ATR) spectrum, which consists of a surface plasmon resonance (SPR) dip and a total internal reflection (TIR) step, is used to determine the optical constant and the thickness of a thin metal film at a given frequency in the conventional Kretschmann configuration. Previous research has shown that two sets of solutions for the optical constant and thickness can be obtained from a SPR dip, and ambiguity should be removed by carrying out another angular scan process or employing a more complicated structure. However, we find that the true solution can be simply selected by a new parameter that denotes the TIR step change. Our method can avoid not only the troubles caused by the double-scan techniques but also the increased difficulties due to the existence of an additional polymer film in a single-scan method.

Numerical Investigation of a Kretschmann-Type Surface Plasmon Resonance Waveguide Sensor

A Kretschmann-type surface plasmon resonance waveguide sensor is analyzed using the wide-angle beam- propagation method (BPM) with the complex Pade approximant and the finite-difference time-domain (FDTD) methods based on the recursive convolution (RC) and piecewise linear RC (PLRC) techniques. The wavelength responses of the sensor are calculated, and a detailed comparison of the numerical results is made. The BPM results are validated through a comparison with the FDTD results, in which the PLRC technique is required in terms of accuracy. The waveguide sensor shows a maximum absorption wavelength shift from 0.609 to 0.623 mum, as the refractive index of an analyte is increased from 1.330 to 1.334, which is comparable to the sensitivity of the conventional Kretschmann configuration.