Kerr beam self-cleaning on the $L{P}_{11}$ mode in graded-index multimode fiber

We report the experimental observation of Kerr beam self-cleaning in a graded-index multimode fiber, leading to output beam profiles different from a bell shape, close to the $L{P}_{01}$ mode. For specific coupling conditions, nonlinear coupling among the guided modes can reshape the output speckle pattern generated by a pulsed beam into the low order $L{P}_{11}$ mode. This was observed in a few meters long multimode fiber with 750 ps pulses at 1064 nm in the normal dispersion regime. The power threshold for $L{P}_{11}$ mode self-cleaning was about three times larger than that required for Kerr nonlinear self- cleaning into the $L{P}_{01}$ mode.