High order harmonic passive mode-locking in double-clad fiber laser

We report passive mode-locking of a soliton erbium-doped double-clad fiber laser operating at the 322
^nd
harmonic of the fundamental cavity frequency. Repetition rates scalable up to 3 GHz have been obtained with a pulse duration of about 1 ps and a pulse energy of about 18 pJ. The supermode suppression at the 322
^nd
harmonic is better than 25 dB. The dynamics of emergence of this operating regime is also presented revealing a very long timescale.