Polarization of Electromagnetic Radiation

Powis Group

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Polarization of Electromagnetic Radiation (Light)

With acknowledgements to Winston Chan (Sarnoff Corp.) for permission to use this Java applet)

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Discussion

The electric field vector of light (electromagnetic radiation) propagating along the positive z direction may be resolved into two perpendicular components, Ex and Ey. The oscillating Ex and Ey electric field components are plotted along z on the right of the applet (above) and will propagate to the right when the animation is started ("GO"). The left graph shows the resultant of these two component field vectors viewed looking towards the source.

Depending on the relative amplitude and phase of the Ex and Ey component fields, the light may be circularly, elliptically or linearly polarized, in the latter cases with the principal axis at any angle φ. Notice the circular polarized light (CPL) consists of two equal amplitude Ex and Ey fields that are exactly ±90° out of phase.

Unfortunately, there is sometimes confusion in the labelling of 'left' and 'right' circular polarization states. The optical convention considers left CPL to be that state with the polarization vector rotating anti-clockwise as viewed looking toward the source. However, this is the opposite of the quantum mechanical convention for labelling helicity, or the projection of the photon angular momentum on the light propagation direction. Some authors fail to distinguish whether the stated handedness of a particular CPL state refers to the helicity or uses the optical convention. Which convention is followed in labelling the CPL buttons in this demonstration?

To Use

A demonstration of a fixed polarization type can be selected by clicking one of the 6 buttons (top) then "GO" to start the animation.

Alternatively it is possible to click and drag on the top of either of the waveforms appearing to the right in order to change the relative amplitude and relative phase of the x and y electric field components. This allows a greater variety of polarization states to be investigated.

For more detailed explanations see the adjacent discussion.