WS2-Clad Microfiber Saturable Absorber for High-Energy Rectangular Pulse Fiber Laser

Tungsten disulfide (WS2), which possesses broadband nonlinear saturable absorption property, displays promising applications in passively mode-locked lasers. Recent research works have demonstrated that WS2 shows much higher thermal conductivity than other transition metal dichalcogenides, which can withstand higher optical intensity and exhibit a higher damage threshold. However, the WS2-based high-energy fiber lasers have not been extensively studied. Here, a WS2-clad microfiber (WCM) saturable absorber (SA) is exploited by an effective transferring approach, which is precisely accomplished under optical microscope. The evanescent field interaction scheme has ability to further raise the optical damage threshold, as well as take full advantage of the nonlinear effect of WS2. Based on the WCM SA, high-energy rectangular pulses are achieved in an Er-doped fiber laser whose pulse duration and energy almost increase linearly with the enhancement of pump power. The maximum energy of single pulse in the cavity can reach 810 nJ under pump power of 800 mW. The experimental results open up venues to create new high-energy laser systems with rich functionalities and novel physical effects.