# On Polarised Light and its State

1. Apr 15, 2016

### JohnGaltis

1. The problem statement, all variables and given/known data
Consider a beam of unpolarised light incident onto air from a crown-glass with a refractive index of 1.52.

Determine the incident angle when the reflected light becomes completely polarised. What is the polarised state of the reflected light?

2. Relevant equations
Brewster's Law: n=tan(theta)

3. The attempt at a solution
I did get 56.7 degrees so that's the incident angle. But from the angle, how do I determine the polarised state?
(One of these right? Linear, Circular and Elliptical)

2. Apr 15, 2016

### Merlin3189

How do you normally get circular/eliptic polarisation?

3. Apr 16, 2016

### ehild

Where is the light incident from? In which medium is the reflected light observed? How is the Brewster angle defined?

4. Apr 16, 2016

### JohnGaltis

Well, the light is incident from the glass. And I suppose that we observe the completely polarised light reflected through air?

Brewster's angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection.

So, at 56.7 degrees, the partially polarised light transmit through the glass while the completely polarised light reflects off the glass. The reflected light is polarised perpendicular to the plane of incidence, I think.

5. Apr 16, 2016

### JohnGaltis

Wait- so it's linearly polarised right? Since the reflected light is polarised only perpendicularly hmm.

6. Apr 16, 2016

### ehild

It is parallel polarized light which is completely transmitted, with no reflection at the Brewster angle.

7. Apr 16, 2016

### ehild

yes, the reflected light is polarized perpendicularly to the plane of incidence.
The incident light was unpolarized, that means, it consisted of equal amount of both parallel and perpendicularly polarized light. If there is no parallel polarized component in the reflected light, only perpendicularly polarized light remains - yes, you are right, it is linearly polarized.
Now there is the angle. What does "n" mean in the formula for the Brewster angle?
If the light arrives from the glass, the reflected light also travels in the glass.

See this http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polref.html