High repetition-rate sub-picosecond source of fibre-amplified vertical-external-cavity surface-emitting semiconductor laser pulses

In this work we used a V-cavity VECSEL with InGaAs quantum-well-based gain and semiconductor saturable absorber mirror structures as described in S. Hoogland et al.(2005): an overall cavity length of 25 mm conferred a fundamental pulse repetition frequency of 5.9908 GHz, and the VECSEL emitted 1-ps pulses in a stable passively mode-locked train with 40 mW average power. Pulses from the VECSEL were then launched through a free space optical isolator into 2 m of Yb-doped fiber with an octagonal core and outer cladding diameters of 20 mum and 125 mum respectively (Liekki Yb 1200-20/125DC). The fiber was cladding-pumped by a 5-W fibre-coupled diode at 915 nm.