BINARY PHASE PLATES CANNOT IMPROVE LASER-BEAM QUALITY

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