Binary phase plates cannot improve laser beam quality

Abstract

Binary phase plates are often suggested as a means for improving the far-field brightness of beams coming from antiphased laser arrays or waveguide lasers operating in higher-order modes. Somewhat surprisingly, however, binary phase plates actually cannot improve at all the second-moment-based beam quality factor M2 as usually defined for such beams. Even from a power-in-the-bucket viewpoint, their usefulness is debatable.