English: In the illustration is the electric field of the linearly polarized light just before it enters the quarter-wave plate. The red line and associated vectors represent how the magnitude and direction of its electric field varies along the direction of travel. For this plane electromagnetic wave, each vector represents the magnitude and direction of the electric field for an entire plane that is perpendicular to the direction of travel. It should be noted that light and all other electromagnetic waves have a magnetic field which is in phase and perpendicular to the electric field being displayed in these illustrations.

To understand the effect the quarter-wave plate has on the linearly polarized light it is useful think of the light being divided into two components at right angles (orthogonal ). Toward this end, the blue and green lines are projections of the red line onto the vertical and horizontal planes respectively and represent how the electric field changes in the direction of those two planes. The two components have the same amplitude and are in phase. Because the quarter-wave plate is made of a birefringent material, when in the wave plate, the light travels at different speeds depending on the direction of its electric field. This means that the horizontal component which is along the slow axis of the wave plate will travel at a slightly slower speed than the component that is directed along the vertical fast axis. Initially the two components are in phase, but as the two components travel through the wave plate the horizontal component of the light drifts farther behind that of the vertical. By adjusting the thickness of the wave plate one can control how much the horizontal component is delayed relative to vertical component before the light leaves the wave plate and they again begin to travel at the same speed. When the light leaves the quarter-wave plate the rightward horizontal component will be exactly one quarter of a wavelength behind the vertical component making the light left hand circularly polarized.

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This image was created using the open source program Inkscape. If you open it using that program the image will still be divided into layers and you will have access to information used to create it. If you need to alter it I would suggest first going to my Wikimedia User page at Dave3457 where information is gathered and other related images are listed.

polarisation