Beam Self-Cleaning of 1.5 m High Peak-Power Spatiotemporal Mode-Locked Lasers Enabled By Nonlinear Compression and Disorder

The realization of beam self-cleaning in a cavity is more challenging than in the outside cavity. The peak power of intracavity pulses needs to be high to reach the threshold of beam self-cleaning, which usually relies on additional diffraction grating to compress pulses in a positive-dispersion cavity. Here, it is first experimentally and numerically demonstrated that self-cleaning can be observed in an all-fiber high peak-power Er-doped spatiotemporal mode-locked (STML) laser at all-negative-dispersion. Through the nonlinear compression of graded-index multimode fiber, the pulses are compressed along with the emergence of beam self-cleaning. Besides, the inherent disorder of multimode fiber accelerates the self-cleaning process. The intracavity pulse energy of approximate to 13 nJ with a pulse duration of 734.5 fs is derived under a highly multimode excitation, with an output pulse energy of 2.33 nJ. The pulse energy is a nearly fourfold improvement over the previous report in all-fiber STML at 1.5 mu m Temporal-dependent characteristics and nonlinear polarization dynamics of beam self-cleaning are also experimentally uncovered. It is demonstrated that the STML fiber laser will enable new insights into nonlinear pulse propagation in cavities and related applications.