Low saturable intensity

Opt. Express 22, 11508–11515 (2014)

High-repetition-rate Q-switched fibre lasers are highly desirable for use in a wide variety of applications, including high-resolution photoacoustic microscopy and the realization of high-performance optical parameter oscillators. Various techniques are being investigated for achieving passive Q-switching using a saturable absorber in fibre lasers. Of these, the use of topological insulators is particularly promising. Now, researchers at Beijing University of Technology in China have obtained high repetition rates and output powers from an erbium-doped fibre laser by using a film of the topological insulator Bi₂Se₃ as a saturable absorber. They realized a low saturable optical intensity of 11 MW cm⁻² at a wavelength of 1,550 nm. They claim this is the lowest saturable intensity obtained to date for a saturable absorber made from a topological insulator and ascribe it to the optimization of the reaction conditions. Using this saturable absorber, they were able to achieve repetition rates in the range 459–940 kHz and a maximum output power of 22.35 mW. The saturable absorber was made from a film consisting of about five to seven layers of regular-shaped Bi₂Se₃ nanoplatelets.