Optical properties resonant phenomena

Nanometals have interesting optical properties [37,73,74]. For example, suspensions of nanoscopic Au particles can be pink, purple, or blue depending on the diameter of the particles [74]. These colors arise from the plasmon resonance absorption of the nanometal particle, a phenomenon we have explored in some detail [37,73]. We have shown that membranes containing Au nanowires like those described here also show this plasmon resonance band, and as a result such membranes can show a wide variety of colors. This absorption in the visible region provides an interesting optical approach for characterizing the Au nanowire-containing membranes. 

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

As described in the article on the theory of surface plasmon resonance, surface plasmons create a surface-bound evanescent electromagnetic wave which propagates along the surface of an active medium (usually a thin metallic film), with the electric field intensity maximized at this surface and diminishing exponentially on both sides of the interface. As a consequence of this property, the phenomenon has been utilized extensively in studies of surfaces and of thin dielectric films deposited on the active medium. Although numerous other optical techniques have also been applied to such systems (e.g. ellipsometry, interferometry, spectrophotometry, and microscopy the surface plasmon resonance (SPR) method has some important advantages over all other optical techniques, as follows. The method utilizes a relatively simple optical system, it has a superior sensitivity, and the complete system of measurement is located on the side of the apparatus that is remote from the sample, and thus there is no optical interference from the bulk medium. Furthermore, the surfaces of the sample need no extra treatment to increase... 

The physics of surface plasmons propagating along a metal/dielectric interface has been studied intensively, and their fundamental properties have been found to be in good agreement with theoretical concepts based upon the plasma formulation of Maxwell s theory of electromagnetism. The phenomenon has been utilized extensively by physical scientists in studies of the properties of surfaces and thin films. Current interest in the properties of thin surface coatings stems partly from increased applications to thin film devices and, in particular, to recent developments in biosensor devices. This article focuses on the characterization of the surface plasmon resonance phenomenon, with emphasis on the conditions of optical excitation of plasmon resonance and the theoretical analysis of different types of surface resonances. 

In Chap. 1 by J. Homola of this volume [1] surface plasmons were introduced as modes of dielectric/metal planar waveguides and their properties were estabhshed. It was demonstrated that the propagation constant of a surface plasmon is sensitive to variations in the refractive index at the surface of a metal film supporting the surface plasmon. In this chapter, it is shown how this phenomenon can be used to create a sensing device. The concept of optical sensors based on surface plasmons, commonly referred as to surface plasmon resonance (SPR) sensors, is described and the main approaches to SPR sensing are presented. In addition, the concept of affinity biosensors is introduced and the main performance characteristics of SPR biosensors are defined. 

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