Energy Absorption in Layered Media

ABSORPTION AND REFLECTION OF INFRARED RADIATION BY ULTRATHIN FILMS 

Harrick [156] and Hansen [99] gained insight into the physics of the ATR spec-tram of a layered stracture and derived formnlas for the penetration depth and the contribntion of the surface layer to the net absorption. Electric field analysis has also been employed to explain the phenomena of SEWs [132, 157, 158] and the excitation of surface polaritons [159, 160], In addition, EEA has been shown to be a basis for an approximate estimation of the molecular orientation (Section 3.11). However, as will be shown below, the MSEEs cannot be used to compare the spectral contrast for the same film in different optical systems. 

In this section, the relationship between the MSEEs and the spectrum contrast will be considered to provide a proper understanding of the IR spectral features discussed in Chapters 2 and 3. The effect of experimental conditions for the three different spectroscopic methods—external reflection, transmission, and ATR — on the MSEEs in a model organic ultrathin film will be examined. The practical implications of these findings will be discussed. 

On the basis of the Poynting theorem (El.18°), the energy loss of the beam with a cross-sectional area of unity in the thin film. A/, after integration of Eq. (1.25) over the volume of this film is given as [99, 101] 

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ENERGY ABSORPTION IN LAYERED MEDIA 49 index of the film at the interface with the surroundings,... 

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