Some of the most interesting nonlinear interactions of electromagnetic fields with elementary excitations of condensed-matter systems occur on extremely fast time scales of only a few femtoseconds (1 fs = 10-15 s). Our group develops novel methods to generate custom-cut optical pulses with tunable center frequencies and spectral components ranging from 0.1 THz (1 THz = 1012 Hz) to >100 THz, peak amplitudes on the order of up to 1 V/Å, and durations down to the single-cycle limit. Time-domain spectroscopy – an oscilloscope for light – detects these waveforms with subcycle precision, giving access to high-order nonlinearities and coherent subcycle dynamics of complex light-matter interactions from the upper GHz regime up to the near-infrared spectral range. This spectroscopy is complemented by tailor-cut THz resonator structures fabricated by electron-beam lithography, enabling us to craft electromagnetic near fields, and to control custom optical nonlinearities on strongly sub-wavelength scales.
Research highlights of our group include high-harmonics generation, coherent nonlinearities beyond Kohn’s theorem, minimally dissipative all coherent spin switching, deep-strong light-matter coupling in specialized THz resonators, and non-adiabatic subcycle switch-off of deep-strong light-matter coupling.