We demonstrate that appropriately designed external cavities can be used to
frequency narrow high-power diode-array bars. Using a commercial 20-W arra
y, we narrow the linewidth to 50 GHz with 14 W of cw output power. A magnif
ying telescope and a cylindrical collimating lens minimize broadening owing
to curvature in the alignment of the diode-array elements. (C) 2000 Optica
l Society of America.