# Difference between polarization and phase

1. Apr 22, 2014

### Choisai

So I know how polaroids and 0.5λ plates work, but does this mean that the polarization of the light and the phase of light are the same, but that the polarization of light is actually a vector description of light? Or something like that? Are these two the same?

2. Apr 22, 2014

### phinds

Think of a graph of a single, simple, sine wave, then take the line and make it a solid wavy rod that you are holding in your hand 6" away from your body and horizontal with the waves going up and down. Now push it another 6" away from you. This changes the phase and does nothing to the polarity. Now twist your wrist so that the waves point at a an angle to the vertical. This changes the polarization but does nothing to the phase. So, no, phase and polarization are not only not the same thing, they have nothing to do with each other. The confusion, I think, comes in when you start talking about multiple waves and circular polarization and phase is brought into the discussion because it has to do with the relationship between TWO waves and the way they combine (which is where vectors come in)

3. Apr 24, 2014

### sophiecentaur

Polarisation and phase are two different aspects of EM waves. The polarisation is the direction of the E field vector and the phase describes the time variation of the oscillation (relative to some reference).

To appreciate how quarter and half λ plates work, you need to sort out the distinction between polarisation and phase. If you want to produce polarised light from unpolarised light, you have to use either a birefringent material, a reflecting surface (Brewster angle etc.) or a (relatively modern) dichroic material that will absorb one particular polarisation component and pass the other.
The Concept Map on the Hyperphysics Site will take you to many of the topics that are relevant here.

With my RF based past, I often think that polarisation is easiest to grasp in terms of radio antennae - which inherently produce waves with a specific polarisation and do not produce the randomly polarised waves that large numbers of light emitting atoms tend to do. There are RF equivalents to all the well known optical devices and their operating principles can be much easier to understand as there are fewer layers of knowledge involved (quantum mechanics, random behaviour of atoms etc. can be ignored).

If you can separate out two quadrature (at right angles) polarised beams then you can change the relative phases of the beams so that the vector sum of the E field has various polarisations. If the phase of one polarisation is chosen to be 90o relative to the other, then the resultant E vector will never be zero amplitude but will rotate around the axis to give circular polarisation.