Linear polarization

Linear polarization

In electrodynamics, linear polarization or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation. See polarization for more information.

Historically, the orientation of a polarized electromagnetic wave has been defined in the optical regime by the orientation of the electric vector, and in the radio regime, by the orientation of the magnetic vector.

Mathematical description of linear polarization

The classical sinusoidal plane wave solution of the electromagnetic wave equation for the electric and magnetic fields is (cgs units)
mathbf{E} (mathbf{r} , t ) = mid mathbf{E} mid mathrm{Re} left { |psirangle exp left [i left (kz-omega t right ) right ] right }

mathbf{B} (mathbf{r} , t ) = hat { mathbf{z} } times mathbf{E} (mathbf{r} , t )

for the magnetic field, where k is the wavenumber,

omega_{ }^{ } = c k

is the angular frequency of the wave, and c is the speed of light.

Here

mid mathbf{E} mid

is the amplitude of the field and

|psirangle stackrel{mathrm{def}}{=} begin{pmatrix} psi_x psi_y end{pmatrix} = begin{pmatrix} costheta exp left (i alpha_x right ) sintheta exp left (i alpha_y right ) end{pmatrix}

is the Jones vector in the x-y plane.

The wave is linearly polarized when the phase angles alpha_x^{ } , alpha_y are equal,

alpha_x = alpha_y stackrel{mathrm{def}}{=} alpha .

This represents a wave polarized at an angle theta with respect to the x axis. In that case the Jones vector can be written

|psirangle = begin{pmatrix} costheta sintheta end{pmatrix} exp left (i alpha right ) .

The state vectors for linear polarization in x or y are special cases of this state vector.

If unit vectors are defined such that

|xrangle stackrel{mathrm{def}}{=} begin{pmatrix} 1 0 end{pmatrix}

and

|yrangle stackrel{mathrm{def}}{=} begin{pmatrix} 0 1 end{pmatrix}

then the polarization state can written in the "x-y basis" as

|psirangle = costheta exp left (i alpha right ) |xrangle + sintheta exp left (i alpha right ) |yrangle = psi_x |xrangle + psi_y |yrangle .

References

  • Jackson, John D. (1998). Classical Electrodynamics (3rd ed.). Wiley. ISBN 0-471-30932-X.

See also

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