Enforcing energy balance in coherently superimposed optical vortices
The generation of optical beams with multiple, mutually-coherent orbital-angular-momentum (OAM) modes using phase gratings is analyzed from the perspective of energy distribution and radial mode composition. We show that phase gratings designed with equally-weighted Laguerre-Gauss (LG) modes will generate beams with uneven energy distribution among OAM components. This unwanted outcome cannot be corrected by adjusting the width of the illuminating beam. We propose a way to design phase gratings that will produce a uniform energy distribution among the constituent OAM states after illumination, while minimizing the content of high radial modes. This method is based on a generalized definition for the LG modes that takes advantage of the freedom to select their radial scales.