Passively Q-switched ytterbium doped fiber laser based on a weak-photothermal saturable absorber

Recently, plasmonic nanocrystals (NCs) have attracted much attention due to their wide applications in bioimaging, photothermal therapy and photonics devices. Compared to other metal NCs, copper NCs show a weak photo-thermal effect, which shows that the copper NCs are a good candidate for nonlinear optical materials. In this paper, we demonstrated a Q-switched fiber laser at 1 μm wavelength by using Cu_1.8S NCs as a saturable absorber (SA). By incorporating the Cu_1.8S SA into an ytterbium doped fiber laser cavity pumped by a 980 nm laser diode, stable passive Q-switching at 1038 nm was obtained for a threshold pump power of 63 mW. On gradually increasing the pump power from 64 mW to 160 mW, the repetition rate of a Q-switched laser increases from 25.7 kHz to 54.5 kHz and the pulse duration decreases from 6.7 μs to 2.33 μs. Our results showed that Cu_1.8S NCs is an effective SA for constructing pulsed lasers with a broadband operating wavelength.