文档介绍：第四章固体材料的宏观光学性质
Overview
The study of the optical properties of materials is a huge field and we will only be able to touch on some of the most basic parts
So we will consider the essential properties such as absorption/reflection/transmission and refraction
Then we will look at other phenomena like luminescence and fluorescence
Finally we will mention applications, in particular optical fibres and lasers
Nature of light
Light is an ic wave:
with a velocity given by c = 1/(00) = 3 x 108 m/s
In view of this, it is not surprising that the electric ponent of the wave should interact with electrons electrostatically
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Many of the electronic properties of materials, information on the bonding, position etc. was discovered using spectroscopy, the study of absorbed or emitted radiation
evidence for energy levels in atoms
evidence for energy bands and band-gaps
photoelectric effect
General description of absorption
Because of conservation of energy, we can say that I0 = IT + IA + IR
Io is the intensity (W/m2) of incident light and subscripts refer to transmitted, absorbed or reflected
Alternatively T + A + R = 1 where T, A, and R are fractions of the amount of incident light
T = IT/I0, etc.
So materials are broadly classed as
transparent:relatively little absorption and reflection
translucent:light scattered within the material (see right)
opaque:relatively little transmission
If the material is not perfectly transparent, the intensity decreases exponentially with distance
Consider a small thickness of material, x
The fall of intensity in x is I so I = -a.
where is the absorption coefficient (dimensions are m-1)
In the limit of x 0, we get
The solution of which is I = I0 exp(–x)
Taking “ln” of both sides, we have:
which is known as Lambert’s Law (he also has a unit of light intensity named for him)
Thus, if we can plot -ln(I) against x, we should find from the gradient
Depending on the mater