what happens when a plane polarized light is incident on a half wave plate? i know what happens in the case of a quarter wave plate but there is no information available about the half wave plate. Please help
Half wave plates have two principal axes. If the light is linearly polarized and the polarization direction coincide with one of the axes of the waveplate, the polarization remains the same. When the polarization direction of the incident light does not coincide with one of the principal axes, the half wave plate will rotate the plane of polarization with twice the angle between the polarization of the incident light and the axes.
For example, if the angle between the polarization of the incident light and the principal axes of the half wave plate is $45^\circ$, the polarization plane will be rotated with $90^\circ$.
A Half wave plate introduces $\pi$ phase shift between $x$ and $y$ components (there is a $\lambda/2$ shift in phase). Hence, we get a rotation of $2\theta$ if incident at an angle of $\theta$