A system for heat treating a weld joint includes a beam generator that produces a beam directed at the weld joint. A beam splitter between the beam generator and the weld joint diverts a portion of the beam along a path. A reflector receives the diverted portion of the beam and directs it to a point at the weld joint. A modulator in the path controls passage of the diverted portion of the beam. A method for heat treating a weld joint includes directing a beam at the weld joint, diverting a portion of the beam, and reflecting the diverted portion of the beam in the direction of the weld joint. The method further includes modulating the diverted portion of the beam to control the passage of the diverted portion of the beam.