Light incident

Relationships between the intensity of incident light, sample thickness, concentration and intensity of transmitted light are embodied in Beer s law and Lambert s law. ... 

RRS Resonance Raman spectroscopy [212, 213] Incident light is of wave length corresponding to an absorption band Enhanced sensitivity... 

One of the most interesting features of the Raman spectmm is its dependence on tire incident light frequency, coj. When Wj is on resonance with the excited electronic state, the scattering process closely resembles a process of absorption followed by emission. However, as Uj is detuned from resonance there are no longer... 

Figure Al.6.15. Schematic diagram, showing the time-energy uncertainty principle operative in resonance Raman scattering. If the incident light is detuned from resonance by an amount Aco, the effective lifetime on the excited-state is i 1/Aco (adapted from [15]).

Nomially the amplitude of the total incident field (or intensity of the incident light) is such that the light/matter coupling energies are sufficiently weak not to compete seriously with the dark matter Hamiltonian. As already noted, when this is tire case, tlie induced polarization, P is treated perturbatively in orders of the total electric field. Thus one writes... 

Equation (B 1,9.11) is valid only for plane polarized light. For unpolarized incident light, the beam can be resolved into two polarized components at right angles to each other. The scattered intensity can thus be expressed as (figure Bl.9.2)... 

The intensity of a spectral absorption band at a given wave length is expressed in terms of absorption or extinction coefficients, dehned on the basis of the Beer-Lambert law. The latter states that the fraction of incident light absorbed is proportional to the number of molecules in the light path, i.e., to the concentration (c) and the path length (1). The law may be expressed mathematically as ... 

The subscript v is attached to both of these intensities as a reminder that the foregoing analysis is based on the assumption of vertical polarization for the incident light beam. The ratio of these intensities gives the fraction of light scattered per molecule by vertically polarized light ... 

The sin 0 terms in Eqs. (10.25) and (10.26) arise from the consideration of polarized light. The light scattered by polarized incident light is also polarized in the same direction, so the term 1 + cos 0 in Eq. (10.30) describes the overall polarization of the scattered light. Before we lose sight of the individual contributions to this, it will be helpful to consider this polarization somewhat further. This is done in the following example. 

From now on we shall describe the scattered light by Eq, (10.30) exclusively, rather than considering the separate components. We shall also consider 0 only in the xy plane, in which case we use the symbol 6 to describe this angle. By convention, the incident light approaches the scattering dipole from 6 = 180°, and the transmitted light leaves the sample at 0 = 0°. 

The real utility of d comes in the analysis of thin films. Consider a substrate of refractive index supporting a thin film of thickness d and refractive index in contact with an internal reflection element (the prism) of refractive index as shown in Figure 24. In this case, d depends on the polarization of the incident light beam and is given by... 

Interference effects, which arise because of the extraordinary uniformity of thickness of the film over the spectrometer sample beam, superimposed on the absorption of incident light by parylene films, can be observed. Experimentally, a sinusoidal undulation of the baseline of the spectmm is seen, particularly in the spectral regions where there is Htde absorption by the sample. These so-called "interference fringe" excursions can amount to some... 

---