Buildup and Real-Time Control of Spatiotemporal Nonlinear Dynamics

Ultrafast multimode fiber lasers enable the high-dimensional control of pulses, which can generate spatiotemporal mode-locking with high peak power and multimode Q-switching with large pulse energy. The buildup dynamics and real-time control of spatiotemporal mode-locking and multimode Q-switching within the same laser cavity are crucial for understanding and manipulating of pulsed lasers. In this work, stable spatiotemporal mode-locking in a nanotube-based all-fiber laser was achieved, where the mode-locking could be switched to multimode Q-switching in real time by injecting feedback energy into the cavity. Furthermore, a unified model of mode-locking and Q-switching was established by optimizing the description of the gain evolution. The numerical simulation exhibits conversion between different states, which was consistent with experimental results. The proposed technique is capable of manipulating laser operation states without the need for changes in the intracavity parameters. It boasts the advantages of a simple structure and high universality, offering a novel approach to achieving flexible and reliable high-dimensional laser sources.