Silver Sulfide Nanoparticles as Saturable Absorber for Q-Switching and Refractive Index Sensor

In this work, Q-switched pulses were achieved by using silver sulfide (Ag2S) films as saturable absorbers. Ag2S nanoparticles (NPs) were synthesized by a hydrothermal method. By inserting the Ag2S film into an erbium-doped fiber laser cavity, Q-switching was realized with a central wavelength of 1558 nm for the first time. Interestingly, by integrating the single mode-multimode-single mode fiber sensing structure into the Q-switched fiber laser, the all-fiber refractive index sensing device was realized based on the principle of multi-mode interference. For alcohols with different refractive indices, the red-shift of the central wavelength could be observed with a sensitivity of 251 nm/RIU. These results confirmed that Ag2S NPs possess great potential in nonlinear optics and optical sensing.