Plasmonic Cu1.8S nanocrystals as saturable absorbers for passively Q-switched erbium-doped fiber lasers

Abstract

We demonstrate a passively Q-switched Yb³⁺/Er³⁺ co-doped fiber (YEDF) laser using a filmy sodium carboxymethylcellulose (NaCMC)-based Cu_1.8S nanocrystals (NCs) saturable absorber (SA). Cu_1.8S NCs SA exhibit a broad absorption band from 600 nm to more than 2500 nm. By placing Cu_1.8S NCs SA into a YEDF laser cavity, stable passively Q-switched laser with a central wavelength of ∼1567.2 nm was achieved at a threshold pump power of ∼1.4 W. On gradually increasing the pump power from 1.4 W to 5.6 W, the repetition rate of Q-switched laser increases from 16.6 kHz to 51.14 kHz and the pulse duration decreases from 8.7 μs to 2 μs. Particularly, we measure the output power of Q-switched lasers based on two types of plasmonic materials, Cu_1.8S NCs and gold nanorods (GNRs). The maximum output power of the Q-switched laser based on Cu_1.8S NCs SA is 3–4 times higher than that based on GNRs SA owing to weak photothermal effect of Cu_1.8S NCs. These results show that Cu_1.8S NCs are promising SAs for constructing high power pulse lasers.