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We report on the realization of narrow linewidth high power DFB diode lasers emitting near 1064 nm in stable longitudinal and lateral single mode. The linewidth is analyzed in dependence of the output power for lasers with cavity lengths of 1 and 2 mm by means of a heterodyne beat note technique. The minimum intrinsic linewidth is 22 kHz FWHM (full width at half maximum, at 100 μ s time scale) for an output power of 150 mW and a cavity length of 2 mm. The minimum total linewidth is mainly determined by technical noise and corresponds to 234 kHz FWHM at an output power of 70 mW. The influence of current noise on the linewidth is investigated and compared for different cavity lengths. Re-broadening at high output power is only observed for the contribution of technical noise to the linewidth. The intrinsic linewidth shows the theoretically expected 1/Pout-dependence at all power levels.