Optical properties attenuation length

Important parameters, characterizing fibre properties, are the attenuation a and numerical aperture NA. The attenuation (Equation 1) represents optical losses caused by absorption or scattering of the light guided through the unit fibre length. It is given by ... 

Extracellular occurrence of MAAs is common in corals where these UV-absorbing compounds are found in the external mucus layer of the colony.163 176 MAA concentrations in mucus layers are closely matched to or occasionally less than the MAA concentrations in the coral tissues, indicating that MAAs are probably passively and nonselectively excreted.176 Consideration of the MAA content and optical path length of the mucus layer ( 1 mm) gives an estimated absorbance efficiency of approximately 7% of incident UV. Such low attenuation of UV radiation probably does not provide substantial protection for the living polyps, and it may be the antioxidant properties of mycosporine-glycine that are more important in the mucus layer (see also Section II.A.10). 

After the axons enter the optic nerve, each fiber is encapsulated with a myelin sheath, formed by a class of cells called oligodendrocytes this sheath decreases the membrane conductance of the axons, increasing the conduction velocity and the length over which impulses can be conducted without severe attenuation. Only at the so-called Ranvier nodes is the myelin sheath interrupted, allowing the impulses to be reinforced by virtue of the gating properties of the local membrane. 

There are two types of optical fibers SM and MM fibers. The important parameters characterizing fiber properties are the core and cladding indices, core diameter, attenuation ot, and numerical aperture (NA). The attenuation represents optical losses caused by absorption or scattering of light propagating through the fiber per unit length, as ... 

The guiding properties of the embedded optical fibres were then assessed using a cut-back measurement set-up. Light was inject into a portion of fibre and its intensity at the output measured with respect to the length of the fibre, and the penalty in terms of attenuation was then compared between embedded and non embedded fibres. 

Several properties of polymers complicate their analysis via VS. First, a problem unique to transmission IR spectroscopy is that polymers are very strong absorbers of IR radiation. Therefore, in order to be within the linear region of Beer s law, an extremely thin polymer film must be used in transmission. A good rule of thumb is to keep the thickness below 5 J,m. While the production of such thin films is possible in the laboratory, it must be remembered that most commonly encountered polymer systems are much thicker than this. As a result, the most commonly used industrial IR techniques are reflectance techniques such as attenuated total reflectance (ATR) or reflection-absorption spectroscopy (RAS), which have much smaller effective optical path lengths, typically on the order 1 lm or below. 

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