The spectrum of the output from an external‐cavity laser containing five discrete diode lasers operating as a coherent ensemble has been shown to correspond to a single mode of the cavity with very narrow linewidth. For cw operation, the linewidth is within the 7.5‐MHz measurement resolution. Pulsed outputs from a low‐level cw baseline are reported for which the single‐mode pulse output is also within the 7.5‐MHz measurement resolution. The measured linewidth of the single‐mode pulse output with no cw output is 9 MHz.