A laser assembly (31) comprises a plurality of spaced apart laser devices (30). A light feedback device (40) forms a resonant external cavity with the laser assembly (31). A dispersive device (36) is positioned to receive light from the laser assembly (31) and to transmit or reflect light to the feedback device (40). An imaging device (32, 35) images primary beams (33) from the laser devices (30) at the dispersive device (36) to form a combined intensity distribution pattern having multiple combined lobes (46A, 46B) corresponding to multiple lobes of the individual primary beams (33), each primary light beam contributing to each combined far-field lobe of the combined intensity distribution pattern by light from a corresponding far-field lobe of that primary light beam. Each laser device (30) lases at a different frequency such that its light is directed by the dispersive device (36) along a preferred direction of the light feedback device (40) to obtain maximum feedback. The primary beams combine to form at least one combined feedback beam (37) reflected back to the laser assembly (31) and at least one combined output beam (38) leaving the apparatus, each combined beam having a common axial direction. The light feedback device (40) provides a different reflectance to light from one off-axis lobe of the said combined intensity distribution pattern than to light from another off-axis lobe of the said pattern.
