Mode-locked thulium fiber laser with MoS₂

Liquid-phase exfoliated 2D material multilayer MoS₂ is transferred onto a gold mirror and its saturable absorption at the 2 µm wavelength region is experimentally observed. This transferred MoS₂ saturable absorber has a modulation depth of 13.6% and a saturation intensity of 23.1 MW cm⁻². This saturable absorber is integrated into a linear Tm³⁺ fiber laser cavity, and stable fundamental-frequency mode-locking operation is realized at 2 µm with pulse energy of 15.5 nJ, pulse width of ∼843 ps, and a repetition rate of 9.67 MHz. The laser spectral width is ∼17.3 nm with a center wavelength of 1905 nm. This first presence of mode-locking with multilayer MoS₂ sheets in the 2 µm wavelength region verifies that multilayer MoS₂ is a good candidate for broadband mode-locking comparable to graphene, as well as a good mode-locker for achieving high pulse energy. (letter)