Apparatus and method for coherently adding laser beams

Abstract

The disclosed apparatus includes a diffraction grating illuminated by a plurality of lasers. Apparatus is provided for summing the plurality of lasers coherently by, (a) phase locking the plurality of lasers and by, (b) diffracting the plurality of beams into a single beam. The diffraction grating has a configuration to generate upon illumination substantially equal intensities of diffraction orders corresponding to the number of lasers while suppressing higher unwanted orders. The phase locking can be accomplished by a single master laser, or by a cavity mirror to generate reference beams. Then, the output beams of the plurality of lasers propagating in the reverse direction are coherently superimposed by that grating. It is preferred that the diffraction grating be binary. Both one and two-dimensional diffraction grating arrays are disclosed. In one embodiment, the phase of the plurality of lasers is locked together by means of a separate injection lock laser, in another embodiment the grating is part of a multielement cavity. In a preferred embodiment, the binary grating is a periodic pattern, where the structure of the periodicity is determined by the number of laser beams. Then, an injection lock laser illuminates that grating and locks together the phases of the plurality of lasers whose beams are to be added. Or, alternatively, a mirror is substituted for the injection lock laser and it provides the illumination beam to the grating which then generates the plurality of beams.