Polarization Measurement

Assume having a laser beam which is horizontal linear polarized. As one measure the sqrt(intensity) transmitted through a rotatable linear polarizer its pattern corresponds to a cosine. Plotting this in a polar coordinate system results in the so called "polarization ellipse". But the result is far away from being a (more or less) horizontal line.

But what does the polarization ellipse tell me?

My problem is that from the polar plot one may interpret that the original beam has E-Field components also in non-horizontal direction. But this is (ideally) not true. But only the polarizator has (excepted for the vertical position) components in horizontal direction leading to a transmitted field.

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And how is the plot called one obtains by means of the measurement ("transmitted intensity of a linear polarized laser beam through a step-wise rotated linear polarizator") described above? –  user21079 Feb 17 at 17:58

The polarization ellipse is not defined as the plot in polar coordinates. The polarization ellipse has $E_x$ and $E_y$ (if $z$ is the axis of propagation) as abscissa and ordinate.

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This is correct, but needs more explanation. Fred indeed had a wrong interpretation of an elliptical polarization. The cosine transmission from the polarizer is not the ellipse when we refer to elliptical polarization. In fact, I have never seen plotted that cosine in a polar plot; it is quite misleading. A cosine that goes from 0 to 1, for example, is a linear polarization. That's clear because the extinction proves there is no component in one axis. For different contrasts of the cosine, you get a non-linear polarization, for example elliptical. –  fffred Jun 18 at 4:16