Terahertz photoconductive antenna

A flat plate made of birefringent material is used to change the polarization state of radiation. A waveplate works by shifting the phase between two vertically polarized components of the wave. The most common types of wave plates are half wave plates (λ/2 plates) and quarter wave plates (λ/4 plates). The λ/2 board provides a phase delay of π, while the λ/4 board provides π/2. A half wave plate changes the polarization direction of linearly polarized light. A quarter wave plate changes linearly polarized light into circular light, and vice versa. If the polarization direction is along one of the axes of the waveplate, the waveplate will not change the polarization of the linearly polarized beam