Passive harmonic mode locking with a high-power ytterbium-doped double-clad fiber laser

We report passive harmonic mode locking of a high-power Yb-doped double-clad fiber laser operating in both the normal- and the anomalous-dispersion regimes with a fundamental repetition rate of 20.4 MHz. In the normal-dispersion regime, 116-fs, 1.7-nJ pulses are emitted at a repetition rate of 102 MHz. The results indicate a supermode suppression of more than 60 dB. In the anomalous-dispersion regime, 1-ps, 125-pJ pulses are emitted at a higher repetition rate of 408 MHz.