Intermodal-beating mode-locking: Toward higher-order harmonic mode-locking of Raman laser

We demonstrate a new mode-locking technique (i.e. intermodal-beating mode-locking, IBML) in Raman fiber lasers to develop high-order harmonic mode-locking. By satisfying the harmonic frequency-matched condition of IBML, the harmonic of mode-locking as high as 680th-order is successfully achieved.