A new method is proposed and considered theoretically for using phase-sensitive amplification as the intensity-discrimination (saturable absorption) element in a laser cavity to generate stable and robust mode-locking. The phase-sensitive amplifier acts as a phase-filter for selecting the specific intensity dependent phase-rotation of the mode-locked pulse that locks the phase to the amplifier pump phase. The nonlinear phase-rotation is analogous to the nonlinear polarization rotation which is used with passive polarizers for mode-locking. It is demonstrated that the phase-sensitive amplification mechanism can indeed result in stable mode-locking. An average cavity model explicitly calculates the stability of the mode-locked pulses.
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