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Unformatted text preview: Dr. P. Lucas U of A MSE 110 Optical properties of materials • When light enters a solid, it can be partly reflected at the surface, transmitted through, absorbed or scattered. • The reflectivity R represent the fraction of incident light reflected at the interface. It increases with the refractive index n: • The refractive index represent the ability of the material to polarize under an oscillating electric field and how this interaction slows down the light wave propagating in a material: • The refractive index of a material increases with density. • In contrast to a glass or a monocrystal, a polycrystalline material appears opaque or translucent due to multiple internal reflection. • The incident electromagnetic wave induces an oscillating electronic cloud which re-emits or scatters light in all directions. • The light scattering efficiency increases for small wavelength and produces the blue color of the sky. SUMMARY FROM LAST CLASS 2 1 1 ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − = = n n I I R o R v c n = = ε o S I a I 4 λ = Dr. P. Lucas U of A MSE 110 Absorption • The absorbance is the fraction of light lost through absorption of photons by atoms in the material. OPTICAL PROPERTIES OF MATERIALS • The magnitude of α ( λ ) is a function of the light wavelength. • Materials only absorb a range of wavelength. • This defines their transparency domain. I o I ℓ • The absorbance is a function of the path length ℓ through the sample and the absorption coefficient α ( λ ) of the material....
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- Spring '08
- Light, Glass, Dr. P. Lucas U, Dr. P. Lucas