Passively Q-switched mid-infrared laser pulse generation with gold nanospheres as a saturable absorber.

High-quality gold (Au) nanospheres (Au-NPs) with a diameter of 52 nm were prepared by the seeded growth method. The mid-infrared (MIR) nonlinear saturable absorption properties were measured by a balanced twin-detector measurement technique. With the as-prepared Au-NPs saturable absorber (SA), an efficient passively Q-switched laser was realized at 2.95 μm for the first time, to the best of our knowledge. Under an absorbed pump power of 4.0 W, a maximum output power of 268 mW was obtained with the shortest pulse width of 734 ns and repetition rate of 91 kHz, corresponding to the pulse energy up to 2.95 μJ. The results indicate that Au-NPs are promising candidates as SAs for MIR laser pulse generation.