Output characteristics regulation of Q-switched fiber laser by Fe3O4 nanoparticle-polyimide film

Abstract Fe3O4 (FO) nanoparticles (NPs) - polyimide (PI) film was used as saturable absorber (SA), and achieved passive Q-switched output at 1.5 μm successfully. Based on the reverse saturable and saturable absorptions of FO NPs-PI film, the laser output characteristics can be further optimized by adjusting the ratio of FO NPs to PI. When the ratio of FO NPs to PI is 1:5 (FO NPs-PI (1:5)), the pulse duration and repetition rate are 0.669 μs and 5.51 kHz; this is the first time to realize the simultaneous compression of repetition rate and pulse duration. The single pulse energy and peak power are up to 364 nJ and 556 mW. The optical conversion efficiency can reach 855%, and it is about two orders of magnitude higher than other reports. The results show that it is helpful to construct high performance Q-switched pulse laser by introducing proper cavity loss through reverse saturable absorption.