# [x-ray physics] refractive index

1. Aug 21, 2008

There doesn't seem to be any difference between

$$n = (1-\delta) - i\beta$$
(the refractive index in the x-ray regime, where $$1-\delta$$ is the real part and $$\beta$$ is the the absorption index)

and

$$n^{\ast} = n - ik$$
(the complex refractive index, where $$n$$ is the refractive index and $$k$$ is the extinction coefficient)

assuming the equivalence $$n = 1-\delta$$ and $$k=\beta$$. I got this from http://henke.lbl.gov/optical_constants/getdb2.html, where I looked up the refractive index of a material. Is there any physical meaning associated with this different notation or it's just a matter of preference? Thanks!