First experimental verification of soliton-like pulse-shaping mechanisms in passively mode-locked VECSELs

During the less than ten years since the first demonstration of modelocked vertical external cavity surface emitting lasers (VECSELs), their performance strongly improved and starts to become comparable to standard modelocked lasers based on ion-doped glasses or crystals. Moreover, the semiconductor gain material has important advantages such as cost-efficient mass-production, emission wavelength and bandwidth control by bandgap engineering. Picosecond pulses with average output powers ≫2 W were achieved and the repetition rate was increased up to 50 GHz [1]. Pulse durations as short as 260 fs were obtained, but only at low power levels of 15 mW [2]. Despite this impressive progress, so far, femtosecond operation could not be combined with high power levels. Previously, the most relevant parameters for the temporal pulse shaping were identified and a qualitative theory on a quasi-soliton pulse shaping mechanism was developed [3]. Here we demonstrate for the first time the detailed experimental verification of this quasi-soliton pulse formation theory. We show that the achievable pulse duration strongly depends on the group delay dispersion (GDD), and that it is important to provide positive overall GDD for achieving short pulse durations.