High-power spectral beam combining based on 890nm laser diode array

Spectral beam combining (SBC) in the fast axis (FA) direction based on the laser diode array (LDA) consisting of eighteen 400 mu m broad-area laser diodes at - 890 nm is demonstrated. For scaling higher output power, it is essential to take into account the catastrophic optical mirror damage (COMD) of the LDA. The gain characteristics have been studied based on the LDA front-facet reflectivity and the output coupler (OC) reflectivity. While the combination of the LDA with 0.5 % front-facet reflectivity and the OC with 3 % reflectivity is adopted, the SBC system delivers an 808 W maximum peak power with 89 % optical-optical conversion efficiency. The beam quality factor beta is measured to be 2.3 in the FA direction. Moreover, an excellent SBC power stability is confirmed at full output power, indicating the power fluctuation of less than 0.8 % (rms) over 60 min.