Drop-Casted Self-Assembled Topological Insulator Membrane as an Effective Saturable Absorber for Ultrafast Laser Photonics

Through employing a cost-effective solvothermal method, ultrathin topological insulator (TI) bismuth telluride (Bi₂Te₃) nanosheets with uniform hexagonal nanostructures had been synthesized. Thanks to the uniformity of few-layer TI dispersion, we are able to adopt the drop-casting approach in order to directly transfer few-layer TI and, therefore, form a self-assembled uniform volatile TI membrane that is suitably deposited onto the end facet of an optical fiber as an effective optical saturable absorber. Its saturable absorption parameters could be deliberately tailored by thinning its thickness by mechanical exfoliation. The incorporation of the as-fabricated saturable absorber inside the fiber laser cavity allows for the operation of either a microsecond or a femtosecond pulse because different saturable absorption parameters can decide whether the fiber laser operates in the mode-locking or Q-switching state. Our work provides a convenient way of fabricating a high-quality TI membrane-based saturable absorber with promising applications for laser operation.