Energy reflected, intensity

Where R is the reflectivity and d is the thickness. Very accurate values of R and T are needed when the absorptance, (id, is small. The technique of photothermal deflection spectroscopy (PDS) overcomes this problem by measuring the heat absorbed in the film, which is proportional to ad when ad 1. A laser beam passing just above the surface is deflected by the thermal change in refractive index of a liquid in which the sample is immersed. Another sensitive measurement of ad is from the speetral dependence of the photoconductivity. The constant photocurrent method (CPM) uses a background illumination to ensure that the recombination lifetime does not depend on the photon energy and intensity of the illumination. Both techniques are capable of measuring ad down to values of about 10 and provide a very sensitive measure of the absorption coefficient of thin films. 

Meaningful ESR or spectral data have not been obtained. Only a band at 29800 cm. , with a shoulder at 27800 cm. can be resolved in the reflectance spectrum of the black compound in KI the energy and intensity both suggest these arise from charge transfer processes. 

For most materials the reflected energy is only 5-10%, but in regions of strong absorptions the reflected intensity is greater. The data obtained appear different from normal tra(nsmission spectra, as derivative-iike bands result from the superposition of the normal extinction coefficient spectrum with the refractive index dispersion (based upon the Fresnel relationships from physics). However, the reflectance spectrum can be corrected by using the Kramers-Kronig (K-K) transformation. The corrected spectrum appears similar to the familiar transmission spectrum. 

Radiation for measurement of radiation energy, emissivity, reflectivity, intensity, etc. 

Reflectivity (symbol, p), (reflectance) - The ratio of the total energy reflected from a surface to total incident on that surface (p = 1 - s - x) for a perfect mirror this approaches 1.0 for a black body the reflectivity is 0. Technically, reflectivity is the ratio of the intensity of the reflected radiation to the total radiation and reflectance is the ratio of the reflected flux to the incident flux. In thermography, the two terms are often used interchangeably. 

When a wave in one material passes through an interface into a second material some energy is reflected and some is transmitted. By considering the continuity of the amplitudes of waves normal and parallel to the interface it can be shown that the reflected intensity is a proportion R of the incident intensity... 

Figure 7.2 Diffraction of spin-polarized low energy electrons (SP-LEED). (a) Schematic description of the experimental phenomenology, (b) Evaluation of the reflected intensities ia depending on the direction of spin polarization (a = -h or —) and magnetization p, = + or —) with respect to the normal of the scattering plane [3].

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