N=n+ik How can I find n and k experimentally? I have composite material and I want to find the n and k to it .
If you are depositing the film in the form of a thin film, you can take transmittance of the film. There are formulas from which you can calculate n and k provided the films are very thin and of high transmittance.
Dear Ali,
You can calculate complex refractive index by computational codes.
I suggest WIEN2k code for you.
There a many ways to find n and k of thin films or solid. The most widely used are spectrophotometric and elipsometric methods. Each of them has his own pros and cons depending on the sample. To answer you question in more details I need some additional information, such as, what is the spectral range you are interested in, are films transparent or diffusive, what is the approximate thickness, what is the type of substrate, is the film homogenous across the thickness etc
Try to check the following paper from sciencedirect.com:
http://www.sciencedirect.com/science/article/pii/S0257897299004120
For theoretical calculation of refractive index,apply:
R= (n-1) ^2+k^2/ (n+1) ^2+k^2.
(a)For R, the Reflectivity, apply:
R+A+T=1.
because the sum of Reflectivity (R), Absorbance (A) and
Transmittance (T) is equal to one. A and T are exp’tlly known.
(b)For k; the extinction coefficient apply:
k= α λ/4π
(c ) For α; the optical absorption coefficient either apply,
α. = 2.303A/t
Or
α = (h. ν -Eg) ^1/2.
depending upon whether the thickness(t) is known or
the band gap (Eg) is given.
For similar characterisation of media one can use the ellipsometry theory and devices under name ellipsometers. Possible also to measure separetely absorbence (by any photometer) and refractometer for the case when index absorbtion is considerably less than index refraction.
index refraction.
Hello sir,
From UV analysis
If you have transmittance data, first you need to calculate the absorption
coefficient (alpha-a)
alpha = 2.303 log (1/T)/t where t-thickness of the sample
then, reflectance(R) in terms of absorption
coefficient (alpha-a)
R = (exp(−at)+(or)-((exp(−at)T -exp(-3at)T+exp(-2at)T2)1/2)/exp(−at)+exp(-2at)T
then
n = (-(R + 1)+(or)- 2R1/2)/R-1
where n is refractive index
I hope this information may help you.
Regards,
Aravind Rudrarapu
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