Spatial phase locking of linear arrays of 4 and 12 wide-aperture semiconductor laser diodes in an external cavity

Spatial phase locking was achieved experimentally for radiation from linear arrays of 4 and 12 wide-aperture multimode semiconductor lasers, This phase locking was attained in an external cavity of 1 < L < 3 cm length with a plane mirror (R = 90%) by diffractive exchange of radiation between neighbouring lasers, An analysis of all possible cavity oscillation eigenmodes (supermodes) was made for a phase-locked array of 4 coupled lasers. The output radiation of this array was characterised by a high degree of coherence (with the contrast of V = 0.9). The angular width (at half-maximum) delta Psi was 1.2 mrad for the fundamental (nu = 1) and highest (nu = 4) supermodes, and 0.8 mrad for the modes with nu = 2 or 3, which corresponded to the diffraction limit. Full supermode selection was achieved in the 4-laser array as a result of the Talbot effect when the cavity length was L = Z(T)/4. The far-field distribution of the radiation was then characterised by the parameters V = 0.98 and delta Psi = 1.2 mrad, The corresponding parameters of a phase-locked 12-laser array were V = 0.93 for the axial propagation zone and delta Psi = 0.46 mrad.