Effective Suppression of Beam Divergence for High-Power Laser-Diode Stack Based on External-Cavity Technique

We demonstrate an off-axis external-cavity configuration designed to effectively suppress the beam divergence of a high-power laser-diode stack. The off-axis external cavity consists of a set of beam-transformation systems and a stripe mirror. Thirty-eight off-axis external-cavity laser diodes are individually formed for the high-power laser-diode stack. At a drive current of 40 A, the divergence angle of the slow axis is reduced from 7.6° without the external cavity to 1.6° with the external cavity. The external-cavity laser-diode stack achieves a cw power output of 45 W, or 72.4% of the cw power output of a free-running laser-diode stack.