Spatiotemporal mode-locking in lasers with large modal dispersion

TL;DR

This paper demonstrates that spatiotemporal mode-locking can be achieved in multimode lasers with large modal dispersion, highlighting the role of intracavity saturable absorbers and revealing a new auto-selection phenomenon.

Contribution

It extends the understanding of spatiotemporal mode-locking to lasers with large modal dispersion, introducing the passive nonlinear auto-selection mechanism and broadening design possibilities.

Findings

STML achieved in multimode lasers with large dispersion

Intracavity saturable absorber counteracts large modal dispersion

Discovery of passive nonlinear auto-selection of single-mode mode-locking

Abstract

Dissipative nonlinear wave dynamics have been investigated extensively in mode-locked lasers with single transverse-mode, whereas there are few studies related to three-dimensional nonlinear dynamics within lasers. Recently, spatiotemporal mode-locking (STML) was proposed in lasers with small modal (i.e., transverse-mode) dispersion, which has been considered to be critical for achieving STML in those cavities because the small dispersion can be easily balanced. Here, we demonstrate that STML can also be achieved in multimode lasers with much larger modal dispersion, where we find that the intracavity saturable absorber plays an important role for counteracting the large modal dispersion. Furthermore, we observe a new STML phenomenon of passive nonlinear auto-selection of single-mode mode-locking, resulting from the interaction between spatiotemporal saturable absorption and spatial gain competition. Our work significantly broadens the design possibilities for useful STML lasers thus making them much more accessible for applications, and extends the explorable parameter space of the novel dissipative spatiotemporal nonlinear dynamics that can be achieved in these lasers.