Abstract: This disclosure provides systems, methods, and apparatus related to optical systems. In one aspect, a method includes: generating a plurality of laser beams; receiving the plurality of laser beams at the point at a diffractive optical element, the diffracting optical element diffracting the plurality of laser beams to generate a plurality of output laser beams including a central laser beam and a plurality of side laser beams; measuring a power of at least two of the plurality of output laser beams generated by the diffractive optical element; determining a phase error in laser beams of the plurality of laser beams from the power of the at least two of the plurality of output laser beams; and changing the phase N?1 laser beams of the plurality of laser beams, with N being a number of the plurality of laser beams.