Y. Bai, N. Bandyopadhyay, S. Tsao, S. Slivken, and M. Razeghi, High power broad area quantum cascade lasers, Applied Physics Letters, vol.95, issue.22, p.221104, 2009.
DOI : 10.1063/1.3270043

S. Hugger, R. Aidam, W. Bronner, F. Fuchs, R. Lösch et al., Power scaling of quantum cascade lasers via multiemitter beam combining, Optical Engineering, vol.49, issue.11, p.111111, 2010.
DOI : 10.1117/1.3498766

B. G. Lee, J. Kansky, A. K. Goyal, C. Pflügl, L. Diehl et al., Beam combining of quantum cascade laser arrays, Optics Express, vol.17, issue.18, p.16216, 2009.
DOI : 10.1364/OE.17.016216

G. Bloom, C. Larat, E. Lallier, M. Carras, and X. Marcadet, Coherent combining of two quantum-cascade lasers in a Michelson cavity, Optics Letters, vol.35, issue.11, p.1917, 2010.
DOI : 10.1364/OL.35.001917

J. R. Leger, G. J. Swanson, and W. B. Veldkamp, Coherent beam addition of GaAlAs lasers by binary phase gratings, Applied Physics Letters, vol.48, issue.14, p.888, 1986.
DOI : 10.1063/1.96648

H. Dammann, Coherent Optical Generation and Inspection of Two-dimensional Periodic Structures, Optica Acta: International Journal of Optics, vol.57, issue.4, p.505, 1977.
DOI : 10.1016/0030-4018(75)90097-8

J. R. Leger, G. J. Swanson, and W. B. Veldkamp, Coherent laser addition using binary phase gratings, Applied Optics, vol.26, issue.20, p.4391, 1987.
DOI : 10.1364/AO.26.004391

J. Cao, J. Hou, Q. Lu, and X. Xu, Numerical research on self-organized coherent fiber laser arrays with circulating field theory, Journal of the Optical Society of America B, vol.25, issue.7, p.1187, 2008.
DOI : 10.1364/JOSAB.25.001187

G. D. Goodno, C. Shih, and J. E. Rothenberg, Perturbative analysis of coherent combining efficiency with mismatched lasers, Optics Express, vol.18, issue.24, p.25403, 2010.
DOI : 10.1364/OE.18.025403

D. Kouznetsov, J. Bisson, A. Shirakawa, and K. Ueda, Limits of Coherent Addition of Lasers: Simple Estimate, Optical Review, vol.84, issue.6, p.445, 2005.
DOI : 10.1007/s10043-005-0445-8

. Fig, Color online) Typical spectrum of a single QCL (blue) and of the external cavity with the DG (red