Light absorption basic relationships

At angles close to 90° the phase shift is at the value yielding a maximum effective field strength. Calculation of absorption coefficients Ap for p-polarized and As for s-polarized light based on the Maxwell equations, assuming a layer of 1 nm of acetone on a reflecting surface, show basically the close relationship between angle of incidence and phase shift (see Fig. 5.46). 

The principle of optical spectroscopy involves the measurement of the amount of light (radiation) that is absorbed by the sample when the radiation interacts with the sample. The most basic method involves the determination of the fraction of the radiation that is actually transmitted through a sample. The aspects of the measurement, and their relationship to the actual absorption of radiation are illustrated in Fig. 56. In this example, 7o is the power of the incident radiation from the infrared light source, and I is the actual amount of radiation transmitted through the sample. The fundamental relationships are provided with Fig. 56, and these form the basis of a fundamental expression that is used to correlate the analytical spectrum with the amount(s) of material(s) present in a sample. This fundamental expression is a simple rendering of the Beer-Lambert-Bouguer law, which is used in one form or another in the quantitative determination of material composition. 

One of the spedfic objectives of studying UV/VIS optical absorption spectra is to obtain data regarding the physical properties of materials. The spectra obtained include the relationship between the light (transmitted, reflected, or refracted) intensity as a function of photon energy E or wavelength 1. The information obtained is important for basic science and its applications, and indudes many valuable constants that can be calculated to present the optical properties of the medium under investigation. This spedrum can also be evaluated to charaderize the polymer blends. 

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