


Question
What is the formula to find the absorption coefficients of materials?
Asked by: Michelle May
Answer
Well, according to 'principles of optics' from Born & Wolf (p614) the absorption coefficient formula is the following:
X=(2Wnk)/c=(4Pik)/L
Where x is the absorption coefficient,W the frequency of
light in the vacuum, c the speed of light in vacuum, l is
the wavelength inside the medium and n and k
are the refractive index and the attenuation index (also called
extinction coefficient) respectively.
The quantities n and K may be easily be expressed in terms of
the material constants (dielectric constant, the electrical
conductivity and the magnetic permeability)
Note that this expression of the absorption coefficient is
a good approximation if the dielectric constant is real and
the excitation frequency is low (long wavelength)
Answered by: Alex Bouhelier, Ph.D Physics, Uni Basel (CH)

