Ultrafast laser pulse (115 fs) generation by using direct bandgap ultrasmall 2D GaTe quantum dots

Two-dimensional (2D) materials have drawn considerable attention for their applications in ultrafast laser pulse generation, owing to their unique optical nonlinearities. However, most of these 2D materials have an indirect bandgap (e.g. MoS2, WS2) or zero bandgap (e.g. graphene). In this study, we report the nonlinear optical properties of a direct bandgap monoclinic structure, gallium tellurium quantum dots (GaTe QDs), and its application as a novel saturable absorber for mode locking laser generation. The fabricated GaTe QDs have an average size of 2.68 nm. This report is the first demonstration showing the generation of ultrafast laser using the 2D GaTe based saturable absorber. This newly developed saturable absorber combines both the advantages of direct bandgap 2D materials and the quantum dot structure. By incorporating the GaTe QD saturable absorber into both Er-doped and Yb-doped fiber lasers, ultrashort pulses with very stable operation at the central wavelengths of 1530.90 and 1030.72 nm are produced, respectively. The measured saturable intensity of the GaTe absorber is 3.1 GW cm(-2) using a 200 fs, 11.8 MHz, 1560 nm pulsed laser source. Additionally, ultrafast laser pulses with a duration of about 115 fs are generated by inserting the GaTe saturable absorber into an Er-doped fiber laser. The experimental results open a new avenue for the use of direct bandgap GaTe QDs in lasers and photonics applications.