Power scaling of a self-mode-locked vertical-external-cavity surface-emitting laser

A typical self-mode-locked vertical-external-cavity surface-emitting laser must operate at the edge of the stable region of the resonant cavity. Its minimal pump spot on the gain chip is used as a soft aperture. By comparing with a continuous-wave (CW) laser, the pulsed laser is focused more tightly on the gain chip due to the Kerr-lens effect. This mitigates cavity loss of the pulsed laser in comparison with the CW laser, such that successive mode-locking can be initiated. The disadvantage of the above method is that the relatively small pump spot, producing relatively large thermal effect, limits the output power of the laser. To address this issue, we propose another method with the work point of the laser moved slightly from the edge of the stable region and the pump spot moderately extended, with a spot of the pulsed laser on the gain chip that could be smaller or larger than that of the CW laser. We achieve stable self-mode-locking with a record average output power of 8.18 W in a V-type resonator, limited by the applied pump power. The pulse repetition rate and width are 0.71 GHz and 1.92 ps, respectively, and the corresponding peak power is 5.6 kW.