Light absorbed within layer

The fraction of light absorbed within the layer is (1 — co)(l — e x). The fraction scattered downward is m(l — p)(l — e x). The total fraction of radiation incident on the layer that is transmitted downward is... 

The method descriptions in most of the pubfished experiments are not detailed enough to allow us to elucidate whether differences in experimental setup are responsible for the observed variability. For example, data on radiation intensity at the surface of the irradiated water layer are not sufficient in the case of optically thick samples where a significant fraction of the light is absorbed within the upper layer of the sample. Accordingly, differences among samples that differ in the fraction of incident light that is absorbed may not be proportional to the photochemical reactivity of the organic matter. 

The cuvette should provide maximum transmission of radiation and definite, precisely known thickness of the light-absorbing layer. Cuvettes of different thicknesses within the range 5 pm - 10 cm are produced. Small cuvettes capable of accepting samples of volumes down to 100 pi are also available. Small volume cuvettes that enable multiple passage of the beam of radiation are of special interest [15]. 

The Kubelka-Munk two flux model predicted significantly different magnitudes of photon flux within the layers of a coating than a model based on the Lambert-Beer law. Equations and calculation methods are described and results are given that illustrate the effect of substrate reflectance, layer thickness and the absorption and scattering of the layer components on the photon flux and the light absorbed at various levels within the coating. 

Method of Calculation. The equations provide a aethod of estiaating the aagnitude of the fluxes at a position x within a layer and the aaount of light absorbed by a section at that position. The effect of initiator concentration ( via K), substrate reflectance (Rg), total layer thickness (L) and the scattering and absorption of light by pigaents ( K and S ) aay all be siaulated by the aodel. 

Figure 6. The calculated aaount of light absorbed as a function of the coefficient K (or concentration of the absorbing species) at three depths within the layer. Paraaeters D=0.1, 5=0.2. Rg=0.5.

The Kubelka-Munkli.) two flux model appears to be superior to a single flux model based on the Lambert-Beer law as it is capable of taking into account the scattering by components in the layer and the reflectance of the substrate. The model can provide estimates of the amount of light absorbed at any point within the coating and predict how this varies with film thickness, concentration of materials and reflectance of the substrate. 

Instead of the dielectric/dielectric interface used in evanescent wave sensors, it is possible to arrange a dielectric/metal/dielectric sandwich layer such that when monochromatic polarized light (e.g., from a laser source) impinges on a transparent medium having a metalhzed (e.g., Ag or Au) surface, light is absorbed within the plasma formed by the conduction electrons of the metal. This results in a phenomenon known as surface plasmon resonance (SPR). When SPR is induced, the effect is observed as a minimum in the intensity of the light reflected off the metal surface. 

For low-energy X-ray measurements, the detector crystal would be provided with a thin light-tight window, usually of beryllium. The high atomic number of Nal (and indeed most gamma-sensitive scintillators) means that X-rays will be completely absorbed within a very thin layer of scintillator. Accordingly, detectors designed for X-ray work will only be one or two millimetres thick. 

In the Schottky barrier solar cell light energy is transmitted into a semiconductor substrate through an extremely thin semitransparent metal layer . The metal and semiconductor are chosen so that the difference in their work functions causes a depletion region and hence an electric field to be produced below the semiconductor surface. Those photons absorbed within the semiconductor produce electron holes pairs which are separated under the action of the electric field and flow to opposite sides of the junction. The separated charge tends to forward bias the junction causing a... 

All incident photons which generate electron hole-pairs within the semiconductor bulk and space charge regions must first pass through the semitransparent metal layer. Photons which are reflected at the air-metal interface or are absorbed within the metal do not contribute to the photo current. It is therefore of utmost importance that the transmittance of light into the semiconductor is made as high as possible. 

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