Enhancement of mid-infrared saturable absorption in TiS ₂ /graphene heterostructure for robust ~2.8 μm passively Q-switched Er:YAP laser

The heterojunction engineering can provide an effective platform for optimizing and synthesizing the properties of nanomaterials. Herein, the TiS 2 powder was synthesized via solid-phase sintering method and the TiS 2 /graphene (TiS 2 /G) heterostructure film with enhanced saturable absorption was developed by using the liquid-phase exfoliation and the layer-by-layer spin-coating techniques. Measurement results at 2.8 μm revealed it exhibited a modulation depth of ~5.7%, an obviously enhancement compared to the ~4.2% of pure TiS 2 film, meanwhile, the saturation intensity was ~0.12 MW/cm 2 , markedly lower than ~0.17 MW/cm 2 of solo TiS 2 device. With this SAM, a robust passively Q-switched Er:YAP bulk laser operating at ~2.8 μm was demonstrated. The maximal signal-to-noise ratio of the stable pulse sequence reached 35 dB at an absorbed pump power of 6.1 W, with a repetition rate of 177.3 kHz, a pulse width of 232 ns and an average output power of 0.42 W. This functional TiS 2 / Graphene heterostructure film can provide an available optical modulator for robust passively Q-switched laser operation in the mid-infrared band.