Quantum dot (QD) semiconductor saturable absorber mirrors (SESAMs) offer a larger design freedom than standard quantum well (QW) SESAMs. QD density, QD growth conditions, number of QD-layers, and post-growth annealing were optimized to independently reduce the saturation fluence and adjust the modulation depth for an antiresonant SESAM that supported for the first time passive modelocking of a vertical external-cavity surface emitting laser (VECSEL) with the same spot size on gain and absorber. The same spot size is a requirement for the modelocked integrated external-cavity surface emitting laser (MIXSEL) concept which enables wafer-scale fabrication of the ultrafast semiconductor laser. The antiresonant SESAM design has low dispersion, is less susceptible to growth errors, and is therefore very promising for short pulse generation and MIXSEL integration.
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