Fresnel equation

[htngwilliam]

Hi everyone

I have some questions about the Fresnel eqn and I hope someone can help me. I have a light source [flourescent] light shining directly onto water. Part of the light will be reflected and part will be transmitted. I am trying to calculate how much light will be reflected and how much light will be transmitted. I am confused why in the fresnel eqn, there is a parallel r and a penpendicular r? where does these 2 components come from?

 

[jedward]

these components occur for virtually all light sources

the r-parallel and the r-perpendicular are the components of the polarization of the incident light from your source.

consider the fluorescent light source as having equal intensities of both components

including these factors accounts for the polarization that occurs due to reflections (except at normal incidence when they are equal)
polarized sun glasses take advantage of the resulting inequality of the reflected light intensity

 

[htngwilliam]

So how do I know how much light is reflected and transmitted? Do I have to sum up the perpendicular and parellel R & T?

 

[jedward]

the intensity of the reflected light for a flat surface of water which has in index of refration of about 1.3 can be calculated for normal incidence using

reflected = incident *(n-1)*(n-1)/(n+1)*(n+1)
% reflected is about 1.7% FOR THE AIR /WATER REFLECTION

typical glass with an index of refration of 1.5 reflects 4% PER SURFACE OR about 8% when two surfaces considered such as for a single pane window

a closer look will show that at some angle one of the polarization will be 100% reflected
examine the equations for the off normal incidence values