The booming fields of antiferromagnetic spintronics and terahertz (THz) magnonics urge to understand the ultrafast dynamics triggered in antiferromagnets by ultrashort stimuli. The interest in ultrafast magnetism of antiferromagnets has led to new and vastly counter-intuitive findings in experimental and theoretical research. We report on the ultrafast spin and lattice dynamics in a rutile antiferromagnet.
Recording complex terahertz pulse shapes in single-shot is needed in various applications, ranging from terahertz time-domain spectroscopy to real-time accelerator diagnostics. Among existing solutions, association of photonic time-stretch with electro-optic detection has been shown to provide the highest repetition rates. However a fundamental bottleneck in time resolution and bandwidth has severely limited those strategies so far. We present here the first demonstration of a time-stretch ADC, that is no more subjected to this time-resolution limit, by using the DEOS (Diversity Electro-Optic Sampling) reconstruction method [1]. Experiments are performed on the ELBE intense Terahertz source.
[1] Roussel et al., Light Science & Applications 11, 14 (2022) https://doi.org/10.1038/s41377-021-00696-2
Complex conductivity of the topological insulator (TI) Bi2 − xSbxTe3 − ySey samples of various thicknesses and chemical compositions is studied by terahertz time-domain spectroscopy method in the range 0.5 to 2.5 THz. For the first time, a decrease in conductivity in the terahertz range has been observed as the chemical composition approaches the Ren’s curve. The generalized approximate expressions are obtained for complex conductivity with account of the lowest Eu1-phonon mode. Calculations of the Fermi energy and concentration of bulk carriers are performed. Based on the experimental data, an estimate of conductance of the topological states is obtained. The results can be useful in developing terahertz devices based on the specific surface transport in TIs.
This talk advertises scattering-type scanning near-field infrared micro-spectroscopy (s-SNIM) in the spectral range of 75 to 1.3 THz [1], as provided by the free-electron laser FELBE, the narrow-band laser-light source at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany. We demonstrate the -independent s-SNIM resolution of a few 10 nm by exploring structured Au samples, Graphene-transistors, meta-materials [2], and local ferroelectric phase-transitions down to LHe [3]. s-SNIM secondly was integrated into a THz pump-probe experiment for the inspection of excited states in structured SiGe samples. We developed a novel demodulation technique with high temporal resolution [4] hence achieving an excellent Signal-to-Noise Ratio. Thirdly using the super-radiant TELBE light source [5], HZDR recently extended the wavelength range down to 100 GHz radiation. We adapted our s-SNIM to this TELBE photon-source as well, achieving an equally high spatial resolution as with FELBE. Moreover, the superb 30-fs temporal resolution of TELBE will allow us to study a multitude of physical phenomena with sub-cycle resolution [5,6], such as spin-structures, magnons and phonon polaritons.
[1] F. Kuschewski et al., Appl. Phys. Lett. 108 (2016) 113102.
[2] S.C. Kehr et al., ACS Photonics 3 (2016) 20.
[3] J. Döring et al., Appl. Phys. Lett. 105 (2014) 053109.
[4] F. Kuschewski et al., Sci. Rep. 5 (2015) 12582.
[5] B. Green et al., Sci. Rep. 6 (2016) 22256.
[6] S. Kovalev et al., Struct. Dyn. 4 (2017) 024301.
An overview is given about the state-of-the-art of superradiant THz sources with a particular emphasize on very recent developments towards compact facilities based on super-conducting RF accelerator technology which enable quasi-cw operation at high repetition rates.
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