Passive coherent beam combining of quantum-cascade lasers with a Dammann grating

An external cavity with a binary phase grating has been developed to achieve the coherent beam addition of five quantum-cascade lasers emitting at 4.65 μm. The combining of these five emitters is achieved by a binary phase grating or Dammann grating able to separate an incident beam into five beams of equal intensities with a 75% efficiency. A CW output power of ~ 0.65 W corresponding to a combining efficiency of 70% with a good beam quality is obtained. More results concerning output power, combining, efficiency stability and beam quality and spectrum are exposed.