The research area “Fundamentals” contains projects that are focused on basic nonlinear phenomena. Here, the key question in each project is clearly motivated by the underlying physics rather than specific materials. The physics of two-photon emission will be addressed by two projects within this area. Project A01 is focused on the two-photon emission in wide-gap materials. Closely related to this is the investigation of parametric processes in single quantum dots (project A03). Nonlinear light emission and parametric down conversion by optical nanoantennas in the regime of plasmonic near field light-matter interaction will be the subject of project A05. In project A04 the physics of polariton gases, which exhibit spontaneous coherence will be investigated. The physics of nonlinear pulse propagation and interaction is subject of the projects A02 and A06. Nonlinear pulse propagation in cubic GaN waveguides will be investigated in project A02 in close to resonance conditions by time of flight and four-wave-mixing experiments. Nonlinearities that appear as a result of ultrafast acoustic excitations will be studied in project A06.