Single-wavelength 5.6 kW direct diode laser with a high-efficiency beam combination

Our group developed a new optical system equipped with a slit mirror to combine the output power from two LD stack modules (30 bars each) and focus them into a single beam. The new device realized a CW output power of more than 3 kW with a transfer efficiency of 92%. Furthermore, by combining beams from two added stack modules to the main optical path using polarization coupling. we have achieved a CW output power of 5.6 kW with a single wavelength of 808 nm. The focused spot size was 2.4 mm x 0.5 mm (the power intensity was 467 kW/cm(2)) at a practical focal length of 100 mm. The transfer efficiency from the LD output to the focal spot was estimated to be 86.5%. The total energy efficiency against the input electricity was approximately 45%. This value is the highest ever reported in a high-power LD applied to material processing, and a full threefold higher than that of the diode-pumped Nd:YAG laser, a device heretofore known to be highly efficient (at around 15%).