Quarter-wave plate
= Quarter-wave plate
{title2=$\delta=\pm\pi/2\pmod{2\pi}$}
A <quarter-wave plate> gives a quarter-cycle <phase retardation>. Equal transmitted <wave amplitudes> initially in <linear polarization> at $45^\circ$ become <circular polarization>; unequal <wave amplitudes> generally give <elliptical polarization>. Reversing the sign reverses the traversal of the same circle.