Observation of transition between multimode Q-switching and spatiotemporal mode locking

We report experimental observation of multimode Q-switching and spatiotemporal mode locking in a multimode fiber laser. A typical steady Q-switching state is achieved with a 1.88 mu s pulse duration, a 70.14 kHz repetition rate, and a 215.8 mW output power, corresponding to the single pulse energy of 3.08 mu J. We find weak spatial filtering is essential to obtain stable Q-switched pulses, in contrast to the relatively stronger spatial filtering for spatiotemporal mode locking. Furthermore, a reversible transition process, as well as a critical bistable state, between multimode Q-switching and spatiotemporal mode locking, is achieved with specific spatial coupling and waveplates sets. We believe the results will not only contribute to understanding the complicated nonlinear dynamics in multimode, fiber-based platforms, but also benefit the development of promising high-pulse energy lasers. (C) 2021 Chinese Laser Press.

Automated summary

The experimental observation of multimode Q-switching and spatiotemporal mode locking in a multimode fiber laser was reported. It was found that weak spatial filtering is essential for stable Q-switched pulses, while stronger spatial filtering is needed for spatiotemporal mode locking. Additionally, a reversible transition process between multimode Q-switching and spatiotemporal mode locking was achieved with specific spatial coupling and waveplates sets. The results contribute to understanding nonlinear dynamics in multimode fiber-based platforms and the development of high-pulse energy lasers.