Coherent combining of two quantum-cascade lasers in a Michelson cavity

We developed a Michelson-type cavity to achieve coherent combining of two quantum-cascade lasers, emitting at around 4.5microm. We report a cw combining efficiency of 85% (up to 91% near threshold) with good beam quality (M(2)<1.4). Despite the interferometric nature of the coupling mechanism, this type of cavity can withstand disturbance from the laboratory environment without significant power fluctuations. Finally, the spectral behavior and the output power dependence on current are explored.