Ultrathin gold nanowires as broadband saturable absorbers for ultrashort pulsed lasers

Ultrathin gold nanowires (UGNWs) with a diameter of ⩽2 nm have attracted much attention because of their high aspect ratios, unusual physical properties and potential applications in nanoelectronics, sensors and photonics. Despite recent advances on UGNWs and the related devices, nonlinear optical properties of UGNWs and their application on photonic devices (e.g. ultrashort pulsed lasers) remain largely unexplored. Here we show that UGNWs can be used as broadband saturable absorbers (SAs) for constructing ultrashort pulsed lasers with an operating wavelength range from near-infrared to mid-infrared (MIR). UGNWs are prepared by using a silane-mediated approach, and then mixed with polyvinyl alcohol to form the UGNWs film. The UGNWs film not only show strong absorption from visible to MIR spectral region (over 25 μm), but also possess the nonlinear saturable absorption properties in the spectral region. As the UGNWs film SA is inserted into an erbium or thulium doped silica fiber laser cavity, stable passively mode-locked lasers at 1562.2 or 1970 nm with a pulse width of a few hundreds of femtoseconds is obtained, respectively. Especially, by inserting the UGNWs film SA into a holmium/praseodymium codoped fluoride fiber laser cavity, stable passively mode-locked laser at 2864 nm is achieved. Our results show that the UGNWs film are promising SAs for constructing broadband ultrashort pulsed lasers.