Q-switched Mode-locking in Er-doped ZBLAN Fibre Lasers using Carbon Nanotube Saturable Absorber and GaSb-based SESAM

Abstract: Mid-infrared fibre 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-fibre Er-doped ZBLAN laser employing an aerosol-synthesised carbon nanotube film. Furthermore, we compare the laser performance with pulse generation using a state-of-the-art GaSb-based SESAM in an identical cavity design. The carbon nanotube saturable absorber enables pulse generation with a minimum duration of 1.32 us and a pulse energy of 1.4 uJ at an average output power of 63.1 mW. In contrast, the SESAM-based laser produces 560-ns pulses with a pulse energy reaching 4.42 uJ and an average power of 138 mW. These results provide new insights into the interplay between saturable absorber properties and mid-IR fibre laser performance, paving the way for next-generation compact ultrafast sources for scientific and industrial applications.