Surface absorption-reflection

In the absence of tabulated or measured properties for a given surface, various options are available. The behavior of a surface can be computed based on fundamental theories, such as Maxwell s electromagnetic wave theory the surface characteristics can be assumed based on extrapolation from the behavior of similar surfaces a model of the surface behavior can be constructed based on simplified assumed surface characteristics or greatly simplified characteristics can be assumed to be accurate enough for use. In the third table in App. A (Table A.7.3), the spectral complex index of refraction data for a number of metals are listed (from Ref. 16), which can be used to determine the surface absorption, reflection, and transmission characteristics as discussed below. 

Surface absorption-reflection A process where energy is absorbed to some degree by a substrate before being reflected. 

Unlike linear optical effects such as absorption, reflection, and scattering, second order non-linear optical effects are inherently specific for surfaces and interfaces. These effects, namely second harmonic generation (SHG) and sum frequency generation (SFG), are dipole-forbidden in the bulk of centrosymmetric media. In the investigation of isotropic phases such as liquids, gases, and amorphous solids, in particular, signals arise exclusively from the surface or interface region, where the symmetry is disrupted. Non-linear optics are applicable in-situ without the need for a vacuum, and the time response is rapid. 

All the analytical methods mentioned to separate, identify, and quantify chlorophylls and derivatives consume time, money, and samples. As alternatives, industries have been employing non-destructive methods for surface color measurements that are not only indirectly related to chlorophyll content, but may also estimate the pigments directly in tissues, leaving the sample intact and enabling serial analyses in a relatively short time. Eood color affects consumer acceptance and is an important criterion for quality control. Color vision is a complex phenomenon that depends on both the total content and number of pigments and also on absorption, reflectance and emission spectra of each compound present. 

Figure 7. Schematic drawing of a silicon internal reflect tion probe for monitoring surface absorption processes. After N. J. Harrick (60).

Surface area Reflectivity Determination of total surface area by heat of absorption Useful in petrographic analyses... 

Assuming a direct path exists between the source and the listener, the listener will first hear the direct sound, followed by reflections of the sound off nearby surfaces, which are called early echoes. After a few hundred milliseconds, the number of reflected waves becomes very large, and the remainder of the reverberant decay is characterized by a dense collection of echoes traveling in all directions, whose intensity is relatively independent of location within the room. This is called late reverberation or diffuse reverberation, because there is equal energy propagating in all directions. In a perfectly diffuse soundfield, the energy lost due to surface absorption is proportional to the energy density of the soundfield, and thus diffuse reverberation decays exponentially with time. The time required for the reverberation level to decay to 60 dB below the initial level is defined as the reverberation time. 

The interactions between light and matter at a surface include absorption, reflection, phase shift, and diffraction. The... 

Some other materials, such as glass and water, allow visible radiation to penetrate to considerable depths before any significant absorption takes place. Radiation through such scmitranspareiu materials obviously cannot be considered to be a surface phenomenon since the entire volume of the material interacts with radiation. On the other hand, both glass and water ace practically opaque to infrared radiation. Therefore, materials can exhibit different behavior at different wavelengths, and the dependence on wavelength is an important consideration in the study of radiative properties such as emissivity, absorptivity, reflectivity, and transmissivity of materials. 

Different types of reflectance spectroscopy depend upon the reflecting behavior of the radiation on the solid. Fig. 8 illustrates various categories used to distinguish techniques for reflecting radiation off solids. Specular reflection spectroscopy is used to measure the reflectance spectrum of a smooth, glossy surface. In reflection-absorption spectroscopy, the radiation passes through a thin surface film on a reflective... 

There are three types of reflectance techniques specular, diffuse and reflection-absorption as illustrated in Figure 9.22. Specular reflectance is applied to samples with smooth and polished surfaces, diffuse reflectance is applied to samples with rough surfaces, and reflection-absorption is applied to IR-transparent thin films on IR opaque substrates. The specular and diffuse techniques are more widely used and are introduced in more detail in the following text. 

Figure 5.44 displays a typical intrinsic absorption by a solid and the theoretical spectral dependencies of the quantum yields as a function of absorption coefficients and surface potentials (Emeline et al, 2003). In essence, the theoretical quantum yields follow the step-like behaviour of the fundamental absorption, differing from each other by the value and direction of the electric field 6 x) in the space-charge region near the surface, as reflected by the surface potential Us-... 

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