Why does reflected light have a 180° phase change from denser media?

[marlon]

Reflected light will experience a 180 degree phase change when it reflects from a medium of higher index of refraction and no phase change when it reflects from a medium of smaller index. This is very well known. However i am wondering why that is ? Can anyone give me some calculations that actually prove this ?

Thanks

marlon

 

[Meir Achuz]

The "Fresnel Relations" in physics-optics give the reflected E' field as
E'=E_{incident}[(n_1-n_2)/(n_1+n_2)] for normal incidence.
This shows the phase change. The FRs are derived in most junior level EM or optics texts. They follow from the BCs on E and H at the interface of two dielectrics.
The transverse components of each are continuous.

 

[dextercioby]

The theory of reflection of light is presented in any textbook of optics.I liked and recommend the bible:M.Born & P.Wolf:"Principles of Optics",any edition,chapter 1,starting with page 36.


Daniel.

 

[marlon]

Guys, if it is so easy why not give me a specific explanation as to why the phase change happens in this particular case ? Dexter, referring to books is useless because i am never going to read that book. I am asking for an explanation and if you cannot give it then don't post just for the sake of posting...Please...

So my question still stands...Anyone who knows the answer ?


regards
marlon

 

[dextercioby]

Marlon,the equation Meir posted states that,for normal incidence,

$$E_{reflected}=E_{incident}\frac{n_{1}-n_{2}}{n_{1}+n_{2}}$$

If $n_{1} < n_{2}$,then $E_{reflected}= - k E_{incident}$ (1)

,where $k=:\frac{n_{2}-n_{1}}{n_{1}+n_{2}}>0$ (2)

Okay.Now,u write,following (1) & (2)

$$E_{reflected}=k E_{incident}e^{i\pi}$$ (3)

Is it any clear?Guess not.I introduce the phases and the polarization vectors,okay,then

$$\vec{E}_{reflected}=\vec{e_{p}}E_{reflected}e^{i\left(\vec{k}_{reflected}\cdot\vec{r}-\omega t\right)}$$ (4)

Using (3),u see where that phase change comes from.

http://scienceworld.wolfram.com/physics/FresnelEquations.html

(For the graph).

Here's a nice course

http://www.ece.rutgers.edu/~orfanidi/ewa/

BTW,it's PHASE.



Daniel.

 

[marlon]

thanks dexter