Femtosecond extreme ultraviolet (fs-XUV) source

• Subject Area: Condensed Matter Physics
• Term: Funded in 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437328598

The femtosecond extreme ultraviolet source requested in this proposal will be the only extreme ultraviolet source for the photoemission experiments planned in the group Experimentelle Physik VI, coherent spin phenomena in solids that is currently being established at the TU Dortmund. The main goal of the group is to control the magnetic and electronic properties of solids on the shortest possible length- and time-scales by minimizing energy dissipations, i.e. by means of coherent effects. In particular, the femtosecond extreme ultraviolet source will be employed in two parallel experimental schemes: i) spin- and angle-resolved photoemission spectroscopy, ii) time-of-flight momentum microscopy. This combination will allow us to perform the cutting-edge spin-, angle- and time-resolved photoemission experiments that are planned in the ERC consolidator project hyControl and in the project B9 of the DFG Collaborative Research Centre TRR 160: “Coherent manipulation of interacting spin excitations in tailored semiconductors” as well. The main goal of hyControl is to achieve coherent control of nano-scale hybrid units that are formed by depositing molecular units on inorganic surfaces. On the other hand, project B9 aims at the ultrafast manipulations of spins in magnetically ordered 2D materials. The on-going research projects, as well as future research activity planned in the group, pose a set of demanding requirements on the femtosecond extreme ultraviolet source. It should be a high power (at least 300 W) and high repetition rate (at least 300 kHz) Yb-based amplified laser system serving simultaneously two pump-probe set-ups. The high power ensures in-parallel operability, while the high repetition rate allows to perform photoemission experiments with high signal-to-noise ratio while circumventing space-charging effects, which typically reduce the energy- and momentum-resolution in time-resolved photoemission experiments. In each pump-probe line the pump beam will be generated by an optical parametric amplifier, while the probe beam will consist of extreme ultraviolet femtosecond photons with energy up to 70 eV. The high photon energies are required to map the band structure of the studied materials throughout the whole Brillouin zone. In addition, in molecular systems, the extreme ultraviolet spectral range is necessary to perform molecular orbital mapping, enhance the cross section and disentangle the photoemission features of the molecules from those of the substrate. The generation of femtosecond extreme ultraviolet pulses requires different components – mainly an amplified laser system connected to a setup for high harmonic generation in noble gases and several compression stages. Such components need to be perfectly tuned with each other in order to achieve the required specifications. This result can be in practice guaranteed only if the whole system is provided by a single company.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Femtosekunden-Extremultraviolettquelle
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Technische Universität Dortmund
• Leader: Professor Dr. Mirko Cinchetti