Specularly reflected light, information

Numerous methods have been used to measure and analyze specularly reflected light. A brief review of general concepts will place these in better perspective. Information in a mono-... 

The specular reflectivity of neutrons, like the analogous light or X-ray reflectivity, from a surface or interface provides information about the neutron refractive index gradient or distribution in the surface region and in a direction orthogonal to the plane. This can often be simply related to a composition or concentration profile in the direction orthogonal to the surface, to provide directly information about adsorption and the structure of the adsorbed layer. 

External reflection techniques like specular reflection and diffuse reflection are less suitable for studying hydrogels. There are a number of disadvantages of external reflection compared to transmission and ATR techniques. First, for the same acquisition time, the signal-to noise ratio is lower than in transmission or ATR. It is difficult to determine the path length of the light inside the sample making quantitative information difficult. 

Ellipsometry was in fact the earliest optical technique to be applied to the study of electrode processes. It involves the determination of the change in polarisation state of an obliquely incident light beam upon specular reflection at a surface. In order to fully define a monochromatic light beam it is necessary, in addition to knowing the frequency, amplitude, and direction of propagation, to include information about the electric and magnetic vectors which describe the polarisation state. Since these vectors are orthogonal and related in amplitude it is, in fact, only necessary to consider one of them, and it is the electric vector that is usually chosen. If this vector lies in a plane then the beam is said to be plane polarized, and further if this plane lies parallel to the plane of incidence at a surface the beam is said to be p-polarised, whereas a beam polarised in a plane perpendicular to the plane of incidence is referred to as s-polarised. For any beam it is possible to resolve the electric vector into its s and p components, and when these components are of the same frequency but different phase and amplitude the beam is said to be elliptically polarised. This name arises from the... 

Other types of energy-matter interactions, such as reflection and scattering, can also occur. Both phenomena can be exploited to extract chemical information. Specular reflectance is simple reflectance from a surface, rvith no interaction between light and the surface and where the angle of reflection equals the angle of incidence. On rougher surfaces, such as powders, the reflection is diffuse because the angles of reflection are randomized. The difference is the same as that... 

In Total Reflection X-Ray Fluorescence Analysis (TXRF), the sutface of a solid specimen is exposed to an X-ray beam in grazing geometry. The angle of incidence is kept below the critical angle for total reflection, which is determined by the electron density in the specimen surface layer, and is on the order of mrad. With total reflection, only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristic X-ray fluorescence radiation. The energy spectrum recorded by the detector contains quantitative information about the elemental composition and, especially, the trace impurity content of the surface, e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. 

There are two kinds of reflectance specular and diffuse. The first is best demonstrated by standing in front of a mirror. One sees himself, essentially Intact, because the light rays which travel from the subject to the mirror and then to the viewer s eyes have not been changed by the mirror they contain the same information before and after reflection. 

The kind of information provided by reflectance-based optical data depends on whether the measurement is specular or nonspecu-lar and on the spectral range involved. Nonspecular (scattered light) data carry Information about macroscopic, spatially resolvable extrinsic features such as pits, scratches, or particulate contamination. The characteristic dimensions of these features must be of the order of or larger than the Rayleigh length 1 - 0.6IX, where X is the wavelength of light. 

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