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Summary form only given. Active harmonically mode-locked fiber lasers producing picosecond pulses at gigahertz repetition rates for communications and precision optical sampling require a mechanism to equalize pulse energies to prevent amplitude fluctuations and pulse dropouts. Recently, it was shown that two-photon absorption (TPA) can limit the peak intensity of Q-switched mode-locking and enhance the stability of continuous-wave mode-locking. In the paper, it is shown that a semiconductor mirror providing TPA in a harmonically mode-locked fiber laser introduces a fast intensity-dependent loss that can equalize pulse energies and reduce pulse dropouts.