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THz Spectroscopy Group
Department of Physics
A detail shot of a laser in the lab in dark green colors. © Nikolas Golsch​/​TU Dortmund

Research focus

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.

Addressing challenging research questions goes hand in hand with the development of advanced experimental technologies. Below, you learn how we push the limits of femtosecond photonics, nanophotonic structures, high-speed synchronous electronics, nanofabrication, and lab automation.

Technologies

White terahertz pulse with 10^-15s written next to it.
Femtosecond optical and THz spectroscopy
“Enter the exciting realm of subcycle spectroscopy and build the world's fastest oscilloscopes, for light. Generate tailor-cut, ultrabroadband, phase-locked pulses of light with THz carrier frequencies and durations of only one optical cycle, and use them to investigate the dynamics of complex materials with sub-cycle precision. Investigate their nonlinear optical response by strong THz and near-infrared or optical fields. ”
Electrodynamics of nanoresonators
“We design, fabricate and employ custom-cut metallic or superconducting nanoresonators which shape electromagnetic fields in space and time on strongly sub-wavelength scales. Our structures have enabled world records of light-matter coupling strengths and pushed THz cavity quantum electrodynamics (c-QED) to new limits, in which we use vacuum fluctuations in the form of virtual photons to shape light-matter coupled modes. Code within a challenging, extensive software framework in which bare-metal numerical performance matters just as much as abstracted languages which translate high-level symbolic math equations to the solver engines, use electron beam lithography to craft structures on the nanometer scale, and delve into the fascinating physics of THz c-QED.”
FPGAs: Cutting-edge, all-programmable high-speed synchronous electronics
“Learn to program electronics rather than software. Command the complex interplay of millions of logic gates to digitize the signals of photodiodes in synchrony with femtosecond laser technology and steer the flow of data”
Stilysed image of an electron beam hitting a stepped surface.
E-Beam Lithography: Development of subwavelength resonator structures
“Design the three-dimensional electromagnetic field properties of terahertz resonator structures and fabricate them with nanometer precision using our scanning electron microscope geared up for lithography - an electron beam lithography system.”
Robotics and automation
“Use and extend our universal measurement software based on python for highly flexible lab automation. Control actuators, piezo positioners, rotation stages as well as measurement devices including our FPGA-based synchronous detection to fully automatize experiments.”
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