Self-mode-locked Alexandrite Femtosecond Lasers with Multi-Ghz Repetition Rates.

We report the laser-diode pumped multi-gigahertz (GHz) self-mode-locked alexandrite femtosecond (fs) lasers for the first time, to the best of our knowledge. Using a simple linear cavity, stable mode-locked laser was achieved with a repetition rate of 3.6 GHz and a pulse width of 237 fs. Additionally, the second-harmonic mode-locked pulse was realized with a repetition rate of 7.5 GHz and a pulse width of 201 fs based on the Fabry–Perot effect generated in the laser cavity. It was observed that this laser possesses advantages of high repetition rate and short pulse width that enable the development of promising applications in modern ultrafast photonics.