Tm3+-Doped Harmonic Dissipative Soliton Mode-Locked Fiber Laser at 1.93 $\mu$ m Based on Tungsten Disulfide in Anomalous Dispersion Regime

We report a harmonic dissipative soliton <inline-formula> <tex-math notation="LaTeX">$1.93~\mu \text{m}$ </tex-math></inline-formula> thulium fiber laser based on a tungsten disulfide (WS₂) saturable absorber (SA) in the anomalous dispersion regime. The multilayer WS₂ nanosheets were prepared by liquid phase exfoliation method and the SA was fabricated by dropping WS₂ solution onto a gold mirror. The transferred WS₂ SA had a modulation depth of 2.5% and a saturation intensity of 0.82 MW/cm². By incorporating the SA into a linear Tm³⁺ fiber laser cavity, harmonic mode-locked dissipative soliton laser was achieved at 1930 nm with the spectral width of 8 nm, the pulse energy of 3 nJ, the pulse width of 3.6 ns, and the repetition rate of 56.3 MHz. Based on the experimental results, it is shown that with the presence of harmonic mode-locking in <inline-formula> <tex-math notation="LaTeX">$2~\mu \text{m}$ </tex-math></inline-formula> wavelength region, the multilayer WS₂ serving as a SA was verified to be a good candidate for broadband high-energy mode-locking. The order of the harmonic dissipative soliton mode-locked pulses remains the same along with the increasing pump power.