INDEX electromagnetic interactions

Interactions with electromagnetic radiation determine the UV, IR, and NMR spectra, refractive index, etc. For such properties, conjugated systems, including aromatic systems, are particularly significant. 

An individual axisymmetric photon wavepacket that propagates in vacuo and meets a mirror surface, should be reflected in the same way as a plane wave, on account of the matching of the electromagnetic field components at the surface. Inside a material with a refraction index greater than that in vacuo, the transmission of the wavepacket is affected by interaction with atoms and molecules, in a way that is outside the scope of the discussion here. 

Looking at the phenomenon of optical absorption by the medium from the viewpoint of classical wave mechanics, we see that the attenuation of electromagnetic radiation can be attributed to the interaction of the oscillating electric vector with the medium. Any phenomenon involving periodic oscillations can be decomposed to real and imaginary components. Thus, the ordinary refractive index n is the real part of the index of refraction n, which can be written as... 

Accounting for the effect of the host material on the interactions between the dipoles involves the refractive index, the relative orientation of the charges, and the local or internal field. The local or internal field problem is associated with the fact that molecules in a host medium occupy a particular volume or a cavity . This cavity description has been used to formalize the description of interactions between dipoles. The region occupied by the molecule results in an additional correction so the field acting on the molecule will be an effective local field rather than the mean macroscopic field. The field acting on the molecule may be an applied electromagnetic field (such as in absorption), the effect of another dipole or a combination of the two. 

The interactions between the molecule and the environment can lead to distortions in the electrical properties due to the susceptibility of the molecules and the properties of the host matrix. The refractive index of the matrix acts as a screening factor, modifying the optical spectra and interaction between charges or dipoles embedded within it. Local field effects change the interaction with an electromagnetic field and should be considered along with orientation factors in the dipolar interaction. 

Optical properties are usually related to the interaction of a material with electromagnetic radiation in the frequency range from IR to UV. As far as the linear optical response is concerned, the electronic and vibrational structure is included in the real and imaginary parts of the dielectric function i(uj) or refractive index n(oj). However, these only provide information about states that can be reached from the ground state via one-photon transitions. Two-photon states, dark and spin forbidden states (e.g., triplet) do not contribute to n(u>). In addition little knowledge is obtained about relaxation processes in the material. A full characterization requires us to go beyond the linear approximation, considering higher terms in the expansion of h us) as a function of the electric field, since these terms contain the excited state contribution. 

Surface plasmon waves (SPW) have been explored almost half a century ago (23, 24). These are surface-bound electromagnetic waves propagating on the dielectric-metal interface. The existence of SPW strongly depends on the refiuctive index of the dielectric medium adjacent to the metal, so it is commonly known that the electromagnetic field of SPW is extended into the medium only to a depth of 200 nm or so (25, 26). Therefore, SPW is very suitable for the measurement of small changes in refractive index of dielectric medium in the vicinity of metal for detecting bio-molecules interaction (26-30). 

The refractive index n of a medium measures the extent of interaction between electromagnetic radiation and the medium through which it passes. It is defined by n = civ. For example, the refractive index of water at room temperature is 1.33, which means that radiation passes through water at a rate of c/1.33 or 2.26 X 10 °cm s . In other words, light travels 1.33 times slower in water than it does in a vacuum. The velocity and wavelength of radiation become proportionally smaller as the radiation passes from a vacuum or from air to a denser medium, while the frequency remains constant. 

The optical properties of ceramics are useful in the ultraviolet, visible, and infrared ranges of the electromagnetic spectrum, and one key quantity used to describe the optical property of a material is the refractive index, which is a function of the frequency of the electromagnetic radiation. Other quantities used to characterize optical performance are absorption, transmission, and reflection these three properties sum to unity and are also frequency dependent. The last three properties govern many aspects of how light interacts with materials in windows, lenses, mirrors, and filters. In many consumer, decorative, and ornamental applications, the esthetic qualities of the ceramic, such as color, surface texture, gloss, opacity, and translucency, depend critically on how light interacts with the material. 

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