Broadband polarization-insensitive saturable absorption of Fe 2 O 3 nanoparticles.

The synthesis and functionalization of transition-metal oxides are one of the most active research areas in advanced materials. As a typical transition-metal oxide, iron oxide has been widely used in lithium-ion batteries, gas sensors, and for water treatment. Herein, we synthesized Fe2O3 nanoparticles by a co-precipitation method that is inexpensive and non-toxic. The Fe2O3 nanoparticles exhibited broadband saturable absorption. Furthermore, thin Fe2O3 polyvinyl alcohol films were prepared to realize Q-switched operations in a ytterbium-doped fibre laser, an erbium-doped fibre laser, and a thulium-doped fibre laser. Attributed to the polarization-insensitive feature of the saturable absorber, Q-switched cylindrical vector beams were also generated based on mode coupling and selection in two-mode fibre lasers. Such Fe2O3 nanoparticles show great promise for use in Q-switching applications of infrared fibre lasers and cylindrical vector lasers.