Q-switched lasing at the 2 µm wavelength induced by Cu_1.8S nanocrystals

In this paper, we first investigated the nonlinear optical properties of Cu_1.8S nanocrystals (NCs) by using Z-scan and balanced twin detector measurement technologies, and then demonstrated a passively Q-switched laser at the 2 µm wavelength. The Cu_1.8S NCs were synthesized by a solventless thermolysis method and then mixed with sodium carboxymethylcellulose to form the Cu_1.8S NCs film. The film exhibited broadband surface plasmon resonance (SPR) absorption from 800 nm to 2000 nm. By incorporating the Cu_1.8S NCs film into a thulium doped fiber laser cavity pumped by a 1570 nm fiber laser, stable passive Q-switching at ∼1975.16 nm was obtained for a threshold pump power of ∼931 mW, and ∼3.4 µs pulse duration with a pulse repetition rate of ∼35.14 kHz was also obtained for a pump power of ∼996 mW. Our results showed that Cu_1.8S NCs is a promising saturable absorber (SA) for pulse laser generation at the 2 µm wavelength.