Giessen works on ultrafast nano-optics and plasmonics, plasmonic and metasurface sensors, femtosecond two-photon 3D-printed micro-optics (on fiber tips and detectors), widely tunable ultrafast/mid-IR sources for molecular sensing, and Rydberg-exciton quantum optics in cuprous oxide. In the broader landscape of NV-centre ensemble quantum sensing (DEER, nano-NMR, T1 relaxometry) operating near pT/sqrt(Hz) sensitivity, this work sits adjacent as a nanophotonic sensing and light-source enabler.