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I'm working on Fresnel equation for calculation of reflection of a light (532 nm) on Iron.

I've got a question: Is metals refractive index always a real number or it can be a complex number?

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Metals refractive index is always complex number (and not only for metals). Imagine part shows the extinction coefficient $k$ - absorption in a material.
Real and imagine part isn't connected.
P.S. For engineering calculations real part sometimes is less than 1.
Theoretically even for Fresnel reflection in dielectric we must use full formula with complex part:

Normal case (90 deg):

$R=\frac{(n-1)^2+k^2}{(n-1)^2+k^2}$
for dielectrics (glasses) in visual diapason $k<<1$ so we don't use it, but u got metal ;-)

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  • $\begingroup$ Thanks sir. You mean for Iron, I should use the both parts ( real and imaginary ) ? can tell me the both parts for Iron? $\endgroup$ – David 2000 Mar 31 '15 at 19:22
  • $\begingroup$ Sir, did you see the link? :) $\endgroup$ – Oleksii Zhyglov Mar 31 '15 at 19:25
  • $\begingroup$ Got it, thanks. n = n +Ki. OK? is ti true? $\endgroup$ – David 2000 Mar 31 '15 at 19:26
  • $\begingroup$ I don't know precisely your metal thickness but I can look for coefficients at work tomorrow. $\endgroup$ – Oleksii Zhyglov Mar 31 '15 at 19:26
  • $\begingroup$ Sir, is it true : n = n + ki $\endgroup$ – David 2000 Mar 31 '15 at 19:27
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The above answer is correct for certain wavelength, for metal, especially for longer wavelength, the refractinve index is complex number. But when wavelength become shorter, to X ray wavelength or even shorter, metal bacome transparent, and might finally have a real refractinve index. See the database: https://refractiveindex.info/

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