Quasi-1D NbTe₄ for Broadband Pulse Generation from 1.0 to 3.0 μm: Bridging the Near- and Mid-Infrared

Quasi-one-dimensional (quasi-1D) transition metal chalcogenides (TMCs), a subclass of low-dimensional materials, have attracted significant attention due to their unique optical and electronic properties, making them promising candidates for nonlinear photonics. In this work, NbTe₄, a quasi-1D transition metal tetrachalcogenide, was synthesized and employed for the first time as a broadband saturable absorber (SA) for pulsed laser applications. The nonlinear optical (NLO) properties of NbTe₄ were systematically characterized at 1.0 μm, 2.0 μm, and 3.0 μm, revealing saturation intensities of 59.53 GW/cm², 14 GW/cm², and 6.8 MW/cm², with corresponding modulation depths of 17.4%, 5.3%, and 21.5%. Utilizing NbTe₄-SA, passively Q-switched (PQS) pulses were successfully generated in the 1.0 μm and 2.0 μm bands, achieving pulse durations of 86 ns and 2 μs, respectively. Furthermore, stable mode-locked operation was demonstrated in an Er-doped fluoride fiber laser at 3.0 μm, yielding a pulse duration of 19 ps. These results establish NbTe₄ as a highly promising broadband SA material for next-generation ultrafast photonic devices and pave the way for the development of other quasi-1D materials in nonlinear optics.