An apparatus includes a diffractive grating configured to receive multiple output beams from an array of laser sources. The apparatus also includes one or more optical elements configured to receive, direct, and focus multiple zeroth-order light beams, where the zeroth-order light beams include portions of the output beams reflected off the diffractive grating. The apparatus further includes a detector configured to receive the zeroth-order light beams from at least one of the one or more optical elements and process the zeroth-order light beams to generate diagnostic information.