Field rotation and polarization properties of the Porro prism.

We investigate the use of the Porro prism and its application as a beam rotator. The Porro prism can reverse a light beam, and the reversed beam is rotated when the Porro prism rotates. As a result of the two total internal reflections in the Porro prism, the field polarization is changed. We present a schematic setup to realize beam rotation without polarization change and power variation. The setup includes a rotatable Porro prism accompanied by a polarized beam splitter, a quarter-wave plate, and a phase compensator. This beam rotator is useful in the measurement of the orbital angular momentum of a helical beam.