Passively Q-switched Er-doped fiber lasers by using gold nanorods as saturable absorbers

The Au Nano-ropes (AuNRs) with aspect ratio of ~5 were synthesized through seed-mediated growth. We measured the absorption spectrum of the AuNRs and the AuNRs had a broad absorption band (800~1600 nm). Furthermore, we measured the nonlinear absorption of the AuNRs and the result indicated that the AuNRs could be used to realize saturable absorption around 1.56 μm. Therefore, passively Q-switching could be achieved by using them. By inserting the AuNRs into the Er-doped fiber laser cavity, stable Q-switched pulses were achieved for a threshold pump power of 30 mW, and the emission wavelength was 1.56 μm. The highest output power of about 6.9 mW and the pulse energy as high as 219 nJ were obtained when the pump power was increased to 205 mW. Our results show the AuNRs are promising saturable absorber(SAs) for pulsed lasers.