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# Physics/Polarization of Light

Question
1) Why do mutually perpendicular polarized light do not interfere?

2) For a light to be polarized, is it necessary that electric field vector of light must be confined to a single plane? If yes then why circularly or elliptically polarized light are called polarized even though their electric field vector is constantly rotating(that is they are not in single plane)?

One last question:
3)According to book,a linearly or plane polarized light, polarized at any arbitrary angle, may be regarded as combination of horizontally and vertically polarized light, with appropriate amplitude, and which are oscillating in phase or 180 deg out of phase.( that is plane polarized light is resultant wave due to superposition of those two mutually perpendicular polarized light)

Now my question is:
Since we know that two mutually perpendicular light do not interfere, how plane polarized light wave can be considered due to superposition of vertically and horizontally polarized light?

Hello Sashi,

1) There are 3 axes to consider. There is the direction of propagation. And there are the directions of the oscillations of electric and magnetic fields which are perpendicular to each other and to the direction of propagation. So if we say that the direction of propagation is along the z axis, then the x and y axes are the directions of the oscillations of the fields. So I believe that explains why 2 beams of mutually perpendicular polarized light do not interfere. Their fields are not oscillating in the same direction.

2) This topic is outside my field of expertise, but I'll take a shot. I believe that in circularly or elliptically polarized light, there is coordination of all the light from the same source going in the same direction. All that light exhibits the same polarization.

3) Let me try to rephrase your question: If vertically and horizontally polarized light beams intersect at right angles, why is interference not observed? To that question I have to say I don't know.

I used these sources in preparing to discuss your questions. I am sorry for the delay in my reply.

http://en.wikipedia.org/wiki/Electromagnetic_wave
http://en.wikipedia.org/wiki/Polarization_(waves)
http://en.wikipedia.org/wiki/Elliptical_polarization

I hope this was a bit of help,
Steve

Physics

Volunteer

#### Steve Johnson

##### Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

##### Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University