Topological temporally mode-locked laser

Mode-locked lasers play a crucial role in modern science and technology. They are essential to the study of ultrafast and nonlinear optics, and they have applications in metrology, telecommunications and imaging. Recently, there has been interest in studying topological phenomena in mode-locked lasers. From a fundamental perspective, such study promises to reveal nonlinear topological physics, and from a practical perspective it may lead to the development of topologically protected short-pulse sources. Despite this promising outlook, the interplay between topological photonic lattices and laser mode-locking has not been studied experimentally. In this work, we theoretically propose and experimentally realize a topological temporally mode-locked laser. We demonstrate a nonlinearity-driven non-Hermitian skin effect in a laser cavity and observe the robustness of the laser against disorder-induced localization. Our experiments demonstrate fundamental point-gap topological physics that was previously inaccessible to photonics experiments, and they suggest potential applications of our mode-locked laser to sensing, optical computing and robust topological frequency combs. The experimental architecture employed in this work also provides a template for studying topology in other mode-locked photonic sources, including dissipative cavity solitons and synchronously pumped optical parametric oscillators.