Phase retarder components are used in laser systems to convert a linearly polarized beam into a
circularly polarized beam. This is often necessary in X-Y cutting systems so as to provide equal cut
quality in all directions of relative motion of the workpiece. In order to convert linear into circular
polarization a total of one-quarter wave, or λ/4 retardation (90°) is required. This may be achieved
using a single λ/4 retarder, or by a combination of two λ/8 retarders.
The majority of phase retarder components used in high power CO2 laser systems are mirrors, treated
with a special coating.