Dear colleague,

please get familiar with the Krames-Kronig relation. This formalism relates the real part of the optical constants ( e.g. the complex refactive index) with the imaginary part and vice versa.

It is no easy task to really do the calculation because you have to know the whole frequency (wave length)  dependence of the  extinction of your sample. For parts of your extinction spectrum where you do not have experimental data you need to use very good approximations.

May be some colleagues, who really have performed Kramers-Kronig calculations may comment on the complexity.

Remark: please search for 'Kramers-Kronig'  in the Reserarchgate database. There are a lot of informations (papers and /comments).

https://www.researchgate.net/file.PostFileLoader.html?id=58b4add1f7b67ee832276b32&assetKey=AS%3A466509685366786%401488235984944

https://en.wikipedia.org/wiki/Refractive_index#Complex_refractive_index

If you can find the reflection (or absorption +transmission), the a Fresnel equation may give a first approximation: R=(n-1)^2/(n+1)^2 where R -- reflectance at normal incidence of the material in air, n -- refractive index of the material

This attached file can help you         

Dear Oualid,

with reference to your docx-file:

where do you get your 2nd formula  (  alpha =1/d*(ln[ ....].  )  from?

May you provide a reference?

I am not familiar with that equation.

Is it only restricted to semiconductors? L Guru Prasad wants to calculate n for polymer material, but not for semiconductor.

 Thanks in advance

Of course dear Gerhard, i can give you a reference of this equation. Several references contain this equation, as far as i know it is generally used for semiconductors, for a polymer i think that it is not valid. But if your material is a semiconducting polymer, I think that you can use this equation.

DOI: 10.1134/S1023193517020045

This is an article contains this equation P144.

Cordially.  

Dear Oualid

With reference to the docx file you provided, how can I get the value of R in 3rd equation to calculate the value of refractive index?

Can I also use the mentioned formula for the material in solution form?

Hello sir,

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