Femtosecond high-power spontaneous mode-locked operation in vertical-external cavity surface-emitting laser with gigahertz oscillation

We realize a femtosecond high-power spontaneous mode-locked operation with gigahertz oscillation in a vertical-external cavity surface-emitting laser under the condition of eliminating the internal and external unwanted reflection. We find that the reflectivity of the output coupler has a significant influence not only on the output power but also on the output pulse duration. With an incident pump power of 20 W, we have achieved 2.35 W of average output power with 778 fs pulse duration at a repetition rate of 2.17 GHz. The shortest pulse duration was 654 fs at an average output power of 0.45 W.