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Highly efficient single-spatial mode lasers with wattlevel output power in the 9xx-nm wavelength range are of great interest for a variety of applications. We experimentally investigate the influence of the mesa widths on the electrooptical properties of ridge-waveguide lasers, based on an extreme double asymmetric epitaxial structure. These properties are, for example, the conversion efficiency and the maximum power of single-lateral mode operation (kink power). At an output power of almost 1 W, single-lateral mode operation with the highest efficiency of 60% was achieved with a 10-μm ridge-width laser. The highest peak efficiency of 62% and the highest output power of 2.7 W with still 59% efficiency were yielded by a laser with a ridge width of 15 μm, at the expense of a slightly deteriorated beam quality due to the involvement of a higher order lateral mode. The kink power of the 10-μm-ridge laser can be further increased by decreasing the front facet reflectivity from 2.5% to 0.5%. [ABSTRACT FROM AUTHOR]