In this work, novel achievements in the field of ultrafast vertical-external-cavity surfaceemitting lasers (VECSELs) are discussed. These devices have the potential to provide a cost-efficient and compact alternative to current ultrafast laser sources for many fields. Many of the potential areas of applications depend not only on short pulses, but also on a high pulse peak power, i.e. a combination of femtosecond pulses and high average output power. In this work, the pulse duration of ultrafast VECSELs was scaled down to the femtosecond regime and experimental results of mode-locked VECSELs operating in the femtosecond regime will be presented. In order to advance into this regime, the underlying principle of passive modelocking of VECSELs, especially the influence of Group Delay Dispersion (GDD), was investigated in more detail. Pulse durations of a few 100 fs and output powers in the Watt range have not been demonstrated so far, but would be an important next step in the development of these lasers. For this reason, the influence of various parameters on the pulse duration was investigated using numerical pulse formation simulations. The simulations show in particular that the saturation fluence of the gain material must be increased in order to attain shorter pulses with higher output power.weiterlesen