Thickness sensor for drying paints using THz spectroscopy.

Optical terahertz technology has, despite its exciting properties, such as transparency of visibly opaque materials, 30 years after its technological breakthrough, not found a widespread application with societal relevance. Main causes are its maturity and costs. If, however, the uniqueness of both THz radiation and time-domain spectroscopy is used to close a technological gap in the right market sector, we here show that successful applications are in reach.

Experimental verification of soliton-like pulse-shaping mechanisms in passively mode-locked VECSELs.

We present a detailed experimental study on the influence of dispersion on the pulse formation in passively modelocked vertical-external-cavity surface-emitting lasers (VECSELs). We have demonstrated that the shortest pulse duration requires slightly positive dispersion to balance the nonlinear phase shift induced by strong semiconductor gain and absorber saturation. This is in contrast to soliton modelocking in ion-doped solid-state lasers - but similarities remain and will be discussed.

Low saturation fluence antiresonant quantum dot SESAMs for MIXSEL integration.

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.