Spectral Bandwidth Narrowing of High Brightness Spectral Beam Combining Diode Laser

We introduce a 5
^x
demagnifying telescope system into an external cavity spectral beam combining and realize a narrow spectrum diode laser combining output by using a nine-emitter 970 nm diode laser mini-bar. With an external feedback mirror of 10% reflectivity, this experiment yields 44-W combined laser power at the operating current of 70 A. The measured M
²
values of the combined laser beam are 12.2 and 2.8 for the slow and the fast axis, respectively. The spectral bandwidth of the combined laser is about 2.7 nm, which is nearly five times narrower than the output spectral bandwidth of 12.1 nm without the 5
^x
demagnifying telescope. To our knowledge, this is the narrowest spectral bandwidth obtained from the spectral beam combining scheme with a short focal length transform lens.