Excitation of Surface Plasmons

One source of EM enhancement may be attributed to the excitation of surface plasmons (SP) in the metal. A plasmon is a collective excitation in which all of the conduction electrons in a metal oscillate in phase. In the bulk, there is essentially only one allowed fundamental plasmon frequency. 

Ronot Trioli, C. Trouillet, A. Veillas, C. Gagnaire, H., Monochromatic excitation of surface plasmon resonance in an optical fibre refractive index sensor, Sens. Actuators A 1996, 54, 589 593... 

The electronic structure and hence optical properties of nanomaterials depend on the core size. For example, nanoparticles of core size >3 nm show surface plasmon resonance, which is due to the excitation of surface plasmons of nanoparticles by light. When the size of gold nanoparticles comes down to around 1 nm, which is equal to the de Broglie wavelength of the conduction electrons, the electronic bands... 

Figure 3. Optical excitation of surface plasmon-polaritons (surface plasmon) by the attenuated...

Hayazawa, N., Ishitobi, H., Taguchi, A., Ikeda, K., Tarun, A., and Kawata, S. 2007a. Focused excitation of surface plasmon polaritons for efhcient held enhancement based on gapmode in tip-enhanced spectroscopy. Jpn. J. Appl. Phys. 46 7995-99. 

One simple explanation for these results was as follows The electric field at a metal vacuum interface can be >10 times larger than in free space when the conditions required for a surface plasma resonance are met (47). Since the Raman cross-section is proportional to the square of the field, surface plasmons could produce enhancements of >10. This enhancement is probably not large enough to explain the tunneling junction results by itself, but an enhancement in signal of a factor of 100 by the excitation of surface plasmons would increase the Raman intensity from near the limits of detectibility. 

THEORETICAL BACKGROUND 2.1. Excitation of Surface Plasmon Modes... 

Surface plasmons, also known as surface plasmon polaritons or packets of electrons, are surface electromagnetic waves that propagate parallel along a metal-dielectric interface [69,70], Surface plasmons exist where the complex dielectric constants of the two media are of opposite sign. The excitation of surface plasmons by light of a wavelength matching the resonant frequency of the electrons is termed surface plasmon resonance (SPR) for planar surfaces and localized surface plasmon resonance where nanometer-sized metallic structures are concerned [71,72],... 

Baltog I, Primeau N, Reinisch R, Coutaz JL (1996) Observation of stimulated surface enhanced Raman scattering through grating excitation of surface plasmons. JOSA B 13 656... 

The collective excitation of the electron cloud of a conductor is known as a plasmon, if the excitation is confined to the surface of the conductor it is known as a surface plasmon. For the excitation of surface plasmons by light, surface roughness or curvature is required. The electromagnetic field of the light at the surface can be greatly increased when the surface plasmon is excited. This results in the amplification of both the incident and scattered and this is the basis of the electromagnetic SERS mechanism [15]. 

FIG. 4.4 ATR setup for the excitation of surface plasmons in Kretsdimium geometry. (As top) A thin metal film (thickness 50 nm) is evaporated into the base of the prism and acts as a resonator driven by the photon field. (As bottom) The resonant excitation of the surface pbsnon wave is seen in the reflectivity irve as a sharp dip at coupling hgfe (B) Setup for the excitation of guided waves. Modes are excited at the (external) an e 0 . 

An experimental setup of an SP microscope suitable for spatiotemporal measurements in an electrochemical environment is depicted in Fig. 51. The working electrode consists of an Ag or Au film of about 50-nm thickness that is evaporated onto a glass prism having a high refractive index. The glass prism permits the excitation of surface plasmons by... 

E. Kretschmann, The determination of the optical constants of metals by excitation of surface plasmons, Z. Phys. 1971, 241, 313-324. www.spreeta.comhttp //www.ti.com/ snc/products /sensors/spreeta.htm... 

The excitation of surface plasmons that occurs at the planar surfaces is denoted as SPR that which occurs at the surface of nanometer-sized metallic stmctures is... 

In this chapter we present an electromagnetic theory of surface plasmons based on theoretical analysis of light propagation in planar metal/dielectric waveguides. The main characteristics of surface plasmons propagating along metal-dielectric and dielectric-metal-dielectric waveguides are introduced and methods for optical excitation of surface plasmons are discussed. 

The most common approach to excitation of surface plasmons is by means of a prism coupler and the attenuated total reflection method (ATR). There are two configurations of the ATR method - Kretschmann geometry [5] and... 

Fig. 21 Excitation of surface plasmons in the Kretschmann geometry of the attenuated...

Another approach to optical excitation of surface plasmons is based on the diffraction of light on a diffraction grating. In this method, a light wave is incident from a dielectric medium with the refractive index on a metal grating with the dielectric constant e, the grating period A and the grating depth q. Fig. 30. 

Fig. 30 Excitation of surface plasmons by the diffraction of light on a diffraction grating...

Fig. 38 Excitation of surface plasmons by a mode of a dielectric waveguide...

The first term Srh depends on the method of excitation of surface plasmons and the modulation approach used in the SPR sensor and is hereafter referred as to the instrumental contribution. Sri2 describes the sensitivity of the effective index of a surface plasmon to refractive index and is independent of the modulation method and the method of excitation of surface plasmons. The sensitivity of surface plasmon to refractive index Sri2 depends on the profile of fhe refracfive index tih and has been analyzed in Chap. 1 of this volume [ 1 ] for the two main types of refractive index changes - surface refractive index change and bulk refractive index change. 

Surface plasmon resonance (SPR) sensors are optical sensing devices that take advantage of the sensitivity of a special type of electromagnetic field, a surface plasmon, to changes in refractive index. SPR sensors can be classified based on the method for optical excitation of surface plasmons and the measured characteristic of the light wave interacting with the surface plasmon. 

In the optical system of an SPR sensor, surface plasmons are excited by a light wave. The excitation of surface plasmons in the SPR sensor results in a change in one of the characteristics of the light wave. Based on which characteristic of the light wave is modulated and used as a sensor output, SPR sensors can be classified as SPR with (i) angular, (ii) wavelength, (iii) intensity, (iv) phase, or (v) polarization modulation. The first three types of modulation (Fig. 2) are used most frequently in today s SPR sensors. 

The enhancement of the electromagnetic fields at the surface of an internally reflecting crystal arise via the excitation of surface plasmon polaritons (SPP) [30] by the incident IR light. These SPPs are collective electronic excitations at metal surfaces and, theoretically, provide a sensitive probe of the optical properties of the interfacial region via resonance with the in-... 

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