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Experimental Physics - Team Prof. Lange

Welcome to the Lange group at TU Dortmund University!

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.




27 August 2020 – Bleaching the blur


Together with the groups of Prof. Dr. Rupert Huber (Regensburg), Prof. Dr. Miriam S. Vitiello (Pisa) and Prof. Dr. Edmund Linfield (Leeds) we developed a new concept for saturable absorbers in the terahertz spectral domain based on ultrastrong coupling of intersubband transitions to the resonant terahertz mode of a microresonator. These new devices could enable passive mode locking of future quantum cascade lasers.

The results have been published in Nature Communications.



10 August 2020 – Behind the veil of nothingness 


In close collaboration with the groups of Prof. Dr. Rupert Huber, Prof. Dr. Dominique Bougeard, and with Prof. Dr. Cristiano Ciuti (Université de Paris), we switched off deep-strong light-matter coupling much faster than a single cycle of light. Our breakthrough provides a very unusual glimpse behind the virtual photon dress of electrons, which helps unravelling the nature of vacuum fluctuations. In the future, even chemical reactions or superconductivity may be triggered merely by abrupt modification of the quantum vacuum.

The results are reported in Nature Photonics and are featured on the cover page of the November 2020 issue.



15 May 2019 – Swiftly switched spins stay cool


Information technology has to be ever faster and more compact. Yet this challenge comes with a price: Performing a task more rapidly costs more energy. In collaboration with the group of Prof. Dr. Rupert Huber (Regensburg), Prof. Dr. Rostislav Mikhaylovskiy, Prof. Dr. Alexey Kimel (Radboud University, Nijmegen) and Prof. Dr. Anatoly Zvezdin (Russian Academy of Sciences, Moscow) we employed ultrashort terahertz pulses to demonstrate the least-dissipative ultrafast magnetic recording to date and to explore its unique properties. The results are an enabling step towards a new generation of information technology which aims to unite maximal energy efficiency and speed.

The results are reported in Nature 569, 383-387 (2019).