Refractive index Terms Links

Mo and Qq e the linear refractive index and absorption coefficient, respectively ( 2) y is the nonlinear refraction coefficient, while (3 is the nonlinear absorption coefficient. By developing the relation between the electric displacement and the electric field and neglecting the terms proportional to ff, one easily obtains the link between these coefficients and the complex third-order nonlinear susceptibility,... 

The method of choice for the determination of these quantities on HDPE resin is gel permeation chromatography. In this chromatographic method a solvent with the dissolved polyethylene flows through a column filled with a porous material. It is usually a gel of cross-linked polymers. Depending upon the size of the polyethylene coils in the solution, they can fit to the pores of the gel, stick there and block them whereby the transport is retarded. Larger polyethylene chains are transported unhindered with the solvent flow. Thus a size-dependent retardation occurs which justifies the other term size exclusion chromatography (SEC). In the chromatogram, which shows polymer concentration (determined for example via optical measurements (refractive index)) as a function of time, the time coordinate corresponds to a polymer molecular mass coordinate and the concentration... 

It is possible to understand many phenomena in optics and spectroscopy in terms of classical models based on concepts of classical electrodynamics. For example, the absorption and dispersion of electromagnetic waves in matter can be described using the model of damped oscillators for the atomic electrons. This model leads to a complex refractive index and to dispersion relations which give the link between absorption and dispersion. It is not too difficult to give a quantum mechanical formulation of the classical results in most cases. The semiclassical approach will be outlined briefly. 

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