Kretschmann Geometry Research Articles

Surface Plasmon Resonance sensor showing enhanced sensitivity for CO_2 detection in the mid-infrared range

We present the first optical sensor based on Surface Plasmon Resonance (SPR) operating in the mid-infrared range. The experimental setup is based on a Kretschmann geometry with Ti/Au layers deposited on a CaF(2) prism where light excitation is provided by a Quantum Cascade Laser (QCL) source. Evidence of SPR is presented and the sensing capability of the system is demonstrated by using CO(2) and N(2) mixtures as test samples. Due to the absorption of CO(2) at this wavelength, it is shown that the sensitivity of this configuration is five times higher than a similar SPR sensor operating in the visible range of the spectrum.

Surface Plasmon Resonance Responses of Au-SnOxNanocomposite Films

AbstractAu-SnOxnanocomposite thin films composed of gold nanoparticles embedded in SnOxmatrix were prepared by pulsed laser deposition technique and their crystal structure, morphology and chemical composition were evaluated by low angle X-ray diffraction, field-emission scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. For the nanocomposite films with high Au percentage, the surfaces of nanocomposite films are very smooth, while for the films with low Au percentage, the films consist of many embedded Au nanoparticles with particle size of 5-20 nm. The XRD results revealed that in the nanocomposite films Au existed in a polycrystalline phase while SnOxin an amorphous phase. Surface plasmon resonance (SPR) responses of the Au-SnOxnanocomposite thin films were investigated as functions of Au percentage and film thickness in the Kretschmann geometry of attenuated total reflection using a polarized light beam at the wavelength of 640 nm. The reflectance minima (SPR dip) of SPR responses of the Au-SnOxnanocomposite films appeared at higher values of incident angle than that of a pure Au film and as the Au percentage decreases the SPR angles shift to higher values and the widths also become broader. The potential use of Au-SnOxnanocomposite films for SPR gas sensing was discussed.

Optical bistability with surface polaritons in layered structures containing left-handed metallic magnetic composites

We present the exact results on optical bistability (including angular and frequency bistabilities) with surface polaritons in layered structures containing left-handed metallic magnetic composite (MMC). The bistable behaviors of the reflected field are revealed for the Kretschmann and Sarid geometries, respectively. The results show that the properties of the angular and frequency bistabilities are quite similar, namely, the optical bistability with the surface polaritons can occur only when the angle or frequency detunings and the substrate’s nonlinear coefficient have the same sign. For the Kretschmann geometry, the surface polaritons can exist in the pass band due to the negative refraction effect. In the Sarid geometry, the excitation of the long-range surface polaritons in the stop band results in a lower optical bistability threshold compared with the Kretschmann geometry. The above conclusions are valid only for the frequency range where the MMC is left-handed.

Time-Resolved Spectroscopy of Laser-Induced Light Emission from an Evaporated Au Film in the Kretschmann Geometry

We have investigated laser-induced light emission from Au film evaporated on the bottom of a hemispherical glass prism in the Kretschmann geometry. Picosecond laser pulses tuned at a photon energy of 1.35 eV were focused onto the Au film from the vacuum side of the prism, and the time- and photon-energy-resolved spectra of light emitted through the prism were measured in a photon energy range from 1.5 to 2.5 eV for a time span of 2 ns by a streak camera operated in synchronization with the laser pulses. The total intensity of emission was proportional to the square of incident laser power, suggesting that the emission is excited via a second order nonlinear optical process. The time-integrated spectrum of the emission was successfully reproduced by the dielectric theory of light emission that treats radiation by surface plasmon polaritons (SPP) confined in this sample structure. Hence we see that the emission is radiated by SPP being excited via the nonlinear optical process. This feature is not consistent with the temporal behavior of emission, i.e., the lifetime of the emission was as long as 240 ps.

In-Situ Infrared Spectroscopy of Buried Organic Monolayers: Influence of the Substrate on Titanium Reactivity with a Langmuir−Blodgett Film

The reactivity of metals vapor deposited onto organic monolayers has historically been correlated to the metal/terminal organic group chemistry. Here we demonstrate that the chemical composition of the substrate unexpectedly plays a significant role as well. In particular, the reactivity of evaporated titanium toward a cadmium stearate Langmuir-Blodgett (LB) film was found to depend on the substrate upon which the LB film was deposited. Infrared spectra taken in a modified ATR (Kretschmann) geometry with a thin Au substrate showed large changes in peak shape, peak position, and peak width in the C-H stretching region, indicating titanium penetration into the LB film and decomposition of the original well-packed monolayer structure. LB monolayers formed on a platinum oxide (PtO(x)) surface showed remarkably small changes after Ti deposition, indicating only a slight increase in disorder and no significant metal penetration into the film. Films on SiO2 substrates showed reactivity between that of Au and PtO(x). These differences in reactivity can be correlated primarily with the amount of available oxygen associated with each substrate, including surface oxide layers and water incorporated within the LB film.

Features of the reflection of TE waves from a nongyrotropic multiferroic slab

The anomalies induced by an anisotropic magnetoelectric interaction in the reflection of a bulk s-polarized wave from the surface of a slab of a nongyrotropic collinear ferroelectric antiferromagnet are investigated in the Kretschmann geometry under the condition that the ferroelectric axis is perpendicular to the interface between media. A number of features of the propagation and localization of TE magnetic polaritons in a ferroelectric antiferromagnetic slab are discussed.

Emission of hybrid organic-inorganic exciton/plasmon mixed states

In this letter the authors experimentally demonstrate the strong coupling regime at room temperature between a surface plasmon and an exciton from an auto-organized quantum well. The sample is formed by a two dimensional layered perovskite-type semiconductor: s(C6H5C2H4–NH3)PbI4, spin coated onto a silver film. The dispersion lines resulting from reflectometry experiments performed at room temperature in the Kretschmann geometry present an anticrossing with a Rabi splitting of 167meV. The emission of the low energy polariton is presented.

Effects of temperature on the surface plasmon resonance at a metal–semiconductor interface

The effects due to elevated temperatures on the surface plasmon (SP) at a metal–semiconductor interface are studied both experimentally and theoretically. In particular, a junction made of silver and amorphous silicon is fabricated and the interfacial plasmon is excited optically via the Kretschmann geometry. Both the reflectance and phase monitoring of the response of the junction have been studied as a function of temperature from 300 K to 380 K. Theoretical simulations have been carried out to understand the observed data, using a previously established model for the temperature-dependent optical constants of the metal, together with empirically fitted data for those of the semiconductor. Reasonable qualitative comparison between experimental data and simulation is obtained. It is found that the strength of the SP at the junction will decrease as temperature increases, and the methodology of the present experiment may provide a way to quantify such a decrease in the operation efficiency of the junction. In addition, it is shown that, by monitoring the resonance angle, such a junction may act as a temperature sensor with sensitivity possibly higher than the previous ones which employed a bare metal film in the Kretschmann geometry.

A Spectroelectrochemical Study of Metal/Polymer Interfaces by Simultaneous In Situ ATR-FTIR and EIS

The environmental stability of a metal / polymer interface is essential for the durability and mechanical stability of constructions in several important areas such as the automotive, offshore, building and aerospace industries. The protective capability of a polymer film is strongly connected to its barrier properties, but the transport of water and corrosive constituents through the polymer and the subsequent processes at the metal surface are complicated to analyse in detail. The surface to be analysed is confined between two media that are impermeable to most probing particles used in conventional analytical techniques. Several methods exist to describe separate parts of the system, but few techniques work atambient pressure and have the capacity to conduct real-time analysis at relevant exposure conditions. In this work, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) in the Kretschmann geometry was successfully employed for systematic studies of metal / polymer interfaces. This technique requires the use of thin metal films deposited on an internal reflection element (IRE). Most studies were performed on aluminium, which is an important structural light-weight material, but also zinc was analysed, being frequently used for corrosion protection of steel. Upon exposure to water and electrolytes, the ATR-FTIR Kretschmann technique was found capable to monitor and to separate early deterioration related processes at the aluminium / polymer interface, including water sorption and transport of ionic species through the polymer film. Other main processes identified were the formation of corrosion products and swelling of the surface-near polymer network. To perform more comprehensive interpretations, a spectro-electrochemical method was further developed for in situ studies of the hidden metal / polymer interfaces. The ATR-FTIR Kretschmann technique was here combined with the complementary acting technique, Electrical Impedance Spectroscopy (EIS). The integrated set-up was able to provide complementary information, with ATR-FTIR Kretschmann being sensitive to the surface-near region and EIS to the whole system. For instance, metal oxidation and delamination processes can be difficult to distinguish by EIS, while on the other hand oxidation and hydration reactions on aluminiumcan be confirmed as IR bands at distinct positions. Delamination and swelling of a polymer both result in negative bands in an IR spectrum, but these processes may be distinguished by EIS as alterations in different frequency regions. While traditional chemical pre-treatments for enhanced hydrolytic stability perform excellent, they are being phased out from industrial applications due to environmental concerns and work health issues. Today there is an intense ongoing research regarding the mechanisms and performance of environmentally friendly pretreatments to develop systems of similar performance, and the analysis of the confined metal / polymer interface is crucial for this development. The capability of the integrated in situ ATR-FTIR Kretschmann and EIS set-up was therefore further applied to systems where a surface pre-treatment had been applied to the metal prior to the organic coating. Studies were first performed on vacuum-evaporated films of zinc treated with a titanium-based conversion coating and further coated with a UV-curing polymer. Alterations of the conversion layer could be detected upon exposure to the electrolyte. Also alkaline-cleaned aluminium coated with an amino-functional silane film and a thermo-curing epoxy top-coat was thoroughlycharacterized by both ATR-FTIR and IRRAS and further investigated upon exposure toelectrolyte and humid air. Changes at the hidden interface were detected upon thermal curingof the epoxy film and during exposure in electrolyte, and the in situ ATR-FTIR Kretschm annanalysis showed a high sensitivity towards alterations in the interfacial region. Complementary studies in the absence of metal could confirm a water uptake within the silane film and water-induced alterations of the siloxane network.

Sensors and inverted resonance on surface plasmons in palladium

The behavior of the resonance curve for surface plasmons in the Kretschmann geometry for palladium is theoretically studied. The existence of inverted resonance in the near-IR region is detected for a thin film of palladium. It is shown that a broadening of the resonance is observed as the frequency of inelastic collisions of electrons in the metal increases and the plasma frequency decreases. Such behavior of the resonance, associated with variation of the optical constants of the metal, can be used in hydrogen sensors based on palladium.

Ultrafast pump-probe surface plasmon resonance spectroscopy of thin gold films

A time-resolved reflection pump-probe method was combined with a surface plasmon resonance technique in Kretschmann geometry for the investigation of ultrafast light-induced processes in thin films. Transient changes in the gold layer's reflectivity were observed when the layer was excited by 3 ps duration pulses with photon energy exceeding the interband transition and by probing with photon energy close to the interband transition. Comparison of the experimental and modeling results has shown that the imaginary part of the dielectric function of gold increases linearly during excitation, whereas the real part remains unchanged. The decay of the light-induced changes has two components. The first component is faster than the pulse duration, and the second is much longer than 1.5 ns; they are related to cooling of the electron plasma and lattice, respectively.

Force of surface plasmon-coupled evanescent fields on Mie particles

Forces acting on Mie particles by surface plasmon-coupled evanescent fields are theoretically analyzed. An expression of the evanescent field produced in Kretschmann (or Sarid) geometry is derived in terms of vector spherical wave functions, while multiple reflections between the Mie particle and the metal boundary are taken into account. The Cartesian components of the force on a Mie particle by the evanescent field are analytically formulated and numerically evaluated. We show that forces are increased by one or two orders at metal boundaries than at dielectric boundaries. For a glass bead, the force normal to the metal boundary is strong compared with the tangential force. For a silver-coated glass bead, the tangential force is greater than (or comparable with) the normal force. The strong tangential force can be useful for rotating submicrometer-sized rotors at a metal boundary and the normal force can keep the rotors close to the metal boundary.

Optical sensing of the initial stages in the growth and development of fibrin clot

Thrombus formation is a surface phenomenon which is always initiated upon a surface. It makes optical surface sensing systems very reasonable and promising tools for its monitoring and study. We evaluated the feasibility to follow the enzymatic conversion of surface-bound fibrinogen by thrombin to fibrin monomer and possible complex formation between surface-bound fibrin monomer and fibrinogen in solution using a surface plasmon resonance (SPR) sensor. For the investigations of optical properties of immobilised molecular layers, the Kretschmann geometry of the attenuated total reflection (ATR) method was utilised. Density of fibrinogen bound to the surface depended on the concentration of fibrinogen in solution during the adsorption process. A fibrinogen monolayer was always formed. Fibrinogen in solution did not bind to surface-bound fibrinogen. Bound fibrinogen converted by thrombin to fibrin monomer interacted (rather slowly) with fibrinogen in solution. The rate of adsorption depended upon immobilised fibrin monomer density, fibrinogen concentration in solution, and on the presence of calcium ions. At low fibrin monomer density, the second layer was formed that contained about the same amount of protein as the first layer, at higher fibrin monomer concentration less than one molecule of fibrinogen per molecule of fibrin monomer was captured.

The surface enhanced second harmonic generation of light from a randomly rough metal surface in the Kretschmann geometry

We present results of perturbative calculations of the second harmonic light generated in the transmission of p-polarized light through a thin metal film with a one-dimensional random surface in the Kretschmann attenuated total reflection (ATR) geometry. The metal film is deposited on the planar surface of a prism through which the light is incident. The back surface of the film is a one-dimensional random surface whose generators are perpendicular to the plane of incidence. It is in contact either with a semi-infinite vacuum or with a semi-infinite nonlinear crystal (quartz). It is shown that when the random surface separates the metal film from vacuum so that the nonlinearity of the film surfaces gives rise to the harmonic light, for a general angle of incidence a dip appears in the angular dependence of the intensity of the transmitted harmonic light in the direction normal to the mean surface. When the second harmonic generation is due to the nonlinearity of the crystal in contact with the metal film, a peak in the angular dependence of the intensity of the transmitted harmonic light occurs in this direction. These dips and peaks are multiple-scattering effects. However, when the angle of incidence is optimal for the excitation of surface plasmon polaritons at the film-vacuum/nonlinear crystal interface the nonlinear mixing of the incident light and the backward propagating surface plasmon polariton leads to an intense peak in the angular dependence of the intensity of the transmitted harmonic light in the direction normal to the mean surface. This peak is already present in the single-scattering approximation.

Evanescent-wave acceleration of femtosecond electron bunches

A 150-fs 800-nm 1-μJ laser was used to excited surface plasmons in the Kretschmann geometry in a 500-Å silver film. Multiphoton excitation results in the emission of femtosecond electron bunches (40 fC) as had been seen before. The electron beam is highly directional and perpendicular to the prism surface. A time-of-flight setup has been used to measure the kinetic-energy distribution of the photoelectrons. Surprisingly, we find that this distribution extends to energies as high as 40 eV. Theoretical calculations show that these high energies may be due to acceleration in the evanescent laser field that extends from the silver film out into the vacuum. These results suggest that femtosecond pulses with more energy per pulse or longer wavelength may be used to accelerate electrons to the keV or even MeV level.

Resonant Properties of Long-Range Surface Plasmons in an Arbitrary Multilayer Structure

In this study, properties of long-range surface plasmons (LRSPs) in an arbitrary multilayer structure have been investigated. We derived an approximation of the reflectivity from Fresnel formulas. Furthermore, the resonant properties of LRSPs have been calculated. As a result of the simulations, we conclude that the difference in resonant angles decreases as the metal thickness increases, and the damping rate obtained from the Sarid geometry is lower than that obtained from the Kretschmann geometry. The resonant half-width obtained from the Sarid geometry is narrower than those obtained from the Kretschmann and Otto geometries. As far as SP chemical sensors are concerned, the system based on the Sarid geometry is better than that based on the Kretschmann or Otto geometry.

A theoretical study of near-field detection and excitation of surface plasmons

Recently, optical near-field techniques have been applied to detect or to excite surface plasmons at vacuum–metal interface. In this paper we propose a theoretical study of those experiments. We firstly describe the formalism, the sample being a multilayered structure with flat interfaces. The incident field and the field in each layer are expressed as 3D plane-wave expansions. The spatial Fourier amplitudes in each layer are linearly connected to the incident ones by transmission matrices. We then apply this formalism to describe the excitation of a surface plasmon in a Kretschmann geometry and its detection by a near-field probe. In the second experiment, the tip was used in the emission mode to excite the surface plasmons, which were thus far-field detected. We describe the experiment using the Bethe–Bouwkamp model for tip emission.

Voltage dependences of the amplitude and phase of reflected radiation in liquid-crystal structures with surface plasmons

The results of a theoretical calculation of the amplitude and phase of p-polarized monochromatic radiation reflected from layered liquid-crystal structures with surface plasmons as a function of the external voltage applied to the structure (in the Kretschmann geometry) are reported.

Effect of the metal film thickness on surface-plasmon-enhanced Raman scattering in an attenuated total reflection experiment

We present the measured dependence of the Raman intensity on the thickness of the metal film in a Kretschmann geometry when surface plasmons are excited. To perform our work, we deposited a Ag film of varying thickness onto a prism, and then we coated it with a thin layer of copper phthalocyanine. We show that the maximum of the Raman signal is achieved for an overall optimization of the coupling at both pump and Stokes frequencies, demonstrating the simultaneous excitation of surface plasmons at these two frequencies.

Nonlinear optical generation from multiple layers of metal-dielectric films.

Second-harmonic generation due to long-range surface plasmons (LRSP's) from a configuration in which a thin metal film is sandwiched between two dielectric layers (the Sarid configuration) is typically more than two orders of magnitude larger than that from the simple Kretschmann geometry. Extension of the Sarid structure into multiple prism/${\mathrm{SiO}}_{2}$/Ag/${\mathrm{SiO}}_{2}$/Ag/${\mathrm{SiO}}_{2}$ layers allows the LRSP's from adjacent silver films to interfere to yield a sharp resonant dispersion curve. Many features can be demonstrated by varying the thicknesses of dielectric and metal films.