Kerr self-cleaning of pulsed beam in an ytterbium doped multimode fiber

We experimentally demonstrate that Kerr spatial self-cleaning of a pulsed beam
can be obtained in an amplifying multimode optical fiber. An input peak power of 500 W
only was sufficient to produce a quasi-single-mode emission from the double-clad ytterbium
doped multimode fiber (YMMF) with non-parabolic refractive index profile. We compare the
self-cleaning behavior observed in the same fiber with loss and with gain. Laser gain
introduces new opportunities to achieve spatial self-cleaning of light in multimode fibers at a
relatively low power threshold.