Q-switched fiber laser based on saturable absorption of ferroferric-oxide nanoparticles

We demonstrate that ferroferric-oxide（Fe3O4） nanoparticles exhibit nonlinear saturable absorption property at1.55 μm, and fabricate two filmy saturable absorbers by embedding the nanoparticles into a polyvinyl alcohol（PVA） film or polyimide（PI） film separately. In the Fe3O4-PVA（Fe3O4-PI） Q-switched fiber laser, the pulse repetition rate increases from 8.5 kHz（5.5 kHz） to 28 kHz（49 kHz） and the pulse duration decreases from 23.5 μs（47 μs） to 6 μs（3.5 μs） by varying the pump power from 25 m W（23 mW） to 150 m W（650 mW）. Experiment results indicate that PI-based saturable absorbers can afford larger powers than PVA-based saturable absorbers, which can be attributed to the higher fusion point of the PI film. The Fe3O4-PI saturable absorber exhibits features of high damage threshold, low cost, and good flexibility, which could be applied in fields of near-infrared pulse generation and frequency conversions.