Q-Switched Mode-Locking in Er-Doped ZrF4-BaF2-LaF3-AlF3-NaF Fiber Lasers Using Carbon Nanotube–Saturable Absorber and GaSb-Based Semiconductor-Saturable Absorber Mirror

Mid-infrared (IR) fiber lasers are crucial for applications in spectroscopy, medical diagnostics, and environmental sensing, owing to their ability to interact with fundamental molecular vibrational bands. However, achieving stable ultrafast pulse generation in this spectral range remains challenging due to the limited availability of robust saturable absorbers. For the first time, we demonstrate Q-switched mode-locking in an all-fiber Er-doped ZrF₄-BaF₂-LaF₃-AlF₃-NaF laser employing an aerosol-synthesized carbon nanotube (CNT) film. Furthermore, we compare the laser performance with pulse generation using a state-of-the-art GaSb-based semiconductor-saturable absorber mirror (SESAM) in an identical cavity design. The CNT-saturable absorber enables pulse generation with a minimum duration of 1.32 μs and a pulse energy of 1.4 μJ at an average output power of 63.1 mW. In contrast, the SESAM-based laser produces 345-ns pulses with a pulse energy reaching 3.84 μJ and an average power of 202 mW. These results provide new insights into the interplay between saturable absorber properties and mid-IR fiber laser performance, paving the way for next-generation compact ultrafast sources for scientific and industrial applications.