One-dimensional Bi_2Te_3 nanowire based broadband saturable absorber for passively Q-switched Yb-doped and Er-doped solid state lasers

The broad saturable absorption of topological insulator Bi2Te3 nanowires is presented for the first time, as well as the passively Q-switched pulse operations on both Yb-doped and Er-doped bulk laser with a bandwidth over about 1.7 μm. Uniform Bi2Te3 nanowires with a large aspect ratio have been synthesized using ultrathin Te nanowires as the template. The broad absorption spectrum from visible to middle infrared reveals a broad optical response. In a 1.0 μm Yb-doped laser, a pulse width of 303 ns with a pulse energy of 1.2 µJ is achieved. While at Er-doped mid-infrared 2.79 μm, the shortest pulse width and largest pulse energy are tested to be 444 ns and 5 µJ, respectively. Those results reveal the topological insulator Bi2Te3 nanowire to be a reliable broad optical switcher for solid state lasers in near- and mid-infrared bands. As far as we know, it is for the first time that TIs based solid state lasers at mid-infrared region are reported. Furthermore, this work can be extendable to explore TIs with other nanstructures for application as optoelectronic devices.