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Gold nanostars as the saturable absorber for a Q-switched visible solid-state laser.

We demonstrated a passively Q-switched visible Pr:YLF laser using the gold nanostars (GNSs) as the saturable absorber (SA). The nonlinear saturable absorption properties at 639 nm were measured, and the modulation and saturable fluence were calculated to be 3% and 0.3  GW/cm2, respectively. With the GNSs SA, the efficient passively Q-switched lasers were obtained at 639 nm and 721 nm, respectively. The maximum output powers and shortest pulse widths were (256 mW, 168 ns) at 639 nm and (238 mW, 198 ns) for 721 nm. To the best of our knowledge, this is the first time there has been a visible bulk pulse laser using the GNSs as the SA. Our work indicates the GNSs could be excellent and promising optoelectronic devices in the visible domain.