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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