The Zero Phase Shift Mirror turns the beam 90° through what could be a long 'beam delivery system' (the part of the laser between the resonator and the cutting head). The distance between the resonator and the cutting head can be up to 12m (in the case of Trumpf) so there may well be a series of zero phase shift mirrors rather than just one or two as we see on my diagram.
Important Parameters
It is crucial that the mirrors have a tight phase shift tolerance as the beam must be bent without the polarization of the beam being changed. If the phase shift of the beam is not tight enough the beam will be misshapen and less efficient in cutting the required material .
90° Phase Retardation Mirror
90° Phase Retardation Mirror is always the final mirror before the cutting head. Its function is to ensure that the beam that meets the kens is circularly polarized. Circular polarization is the most efficient for the cutting action as it means that there is a beam, which is completely symmetric around the center and hence, has the same cutting strength in each direction. The 90° phase retarder can totally eliminate the ragged cut which can caused by a beam which is not completely, circular and hence, less efficient for the cutting process.
Important Parameters
This is crucial to ensure that the beam uses indeed accurately circularly polarized. Any shift away from the 'perfect' circular polarization will result in a less than perfectly efficient beam for cutting and will result in an uneven cut.
