Parity-time (PT) symmetry is one of the most important accomplishments in optics over the past decade. Here the concept of PT mode-locking (ML) of a laser is introduced, in which active phase-locking of cavity axial modes is realized by asymmetric mode coupling in a complex time crystal. PT ML shows a transition from single-to double-pulse emission as the PT symmetry breaking point is crossed. The transition can show a turbulent behavior, depending on a dimensionless modulation parameter that plays the same role as the Reynolds number in hydrodynamic flows. (C) 2016 Optical Society of America
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