# Interfence of polarized light

1. Feb 20, 2008

### babblingsia

What happens if two waves polarised in the x and y direction , say, interfere? Will the interference pattern be of less intensity? Or will there be a sharper pattern?

2. Feb 21, 2008

### pam

Two light waves, polarized in orthogonal directions, do not interfere in intensity.
The subsequent polarization MAY be affected, if the two waves were prepared coherently.

3. Feb 22, 2008

### Yoni

I don't understand, taking a polarized coherent light beem spiliting it into two, shifting the polarization of one by 90 degrees. Will the interference pattern be reduced?
What do you mean by subsequent polarization MAY be affected?

4. Feb 22, 2008

### pam

I the case you describe, if the path length of the two beams is the same, the result will be a wave polarized at 45 degrees to each original polarilzation.
The intensity will be the same as the original beam.

5. Feb 22, 2008

### babblingsia

I guess I did not frame my question clearly.What I meant is this: Consider the double slit experiment, where in you get an interference pattern on the screen. Suppose the two beams from the slits were polarised in orthogonal direction, in what way would it change the interference pattern? Would you get a sharper image?

6. Feb 22, 2008

### rahuldandekar

Did you get this question from JEST? Just curious, since it came in JEST this year. And you live in India ;).

Well, I myself think there would be no interference pattern. Remember how interference occurs... superposition of waves. If waves in orthogonal directions cannot superpose to form a zero of intensity, they won't "interfere" as such, they'll only combine. Like a vector along x axis can subtract a vector along the same axis, but two vectors along x- and y- axes can only act independently, and never "subtract".

One more way of seeing this is to know that the waves don't interfere if the intensity of the pattern is the sum of the intensities of both the waves (Feynman, the first chapter on QM). E2 = E12 + E22

That's precisely how orthogonal vectors add.

I myself gave the answer as "no interference pattern". :)

7. Feb 23, 2008

### pam

Didn't my post #2 say there would be no interference pattern?

8. Feb 23, 2008

### rahuldandekar

I just tried to explain it more elaborately. :)