The Young Investigators Group led by Jan Rothhardt is based at the Helmholtz Institute Jena and the Institute of Applied Physics. It focuses on the development and applications of high photon flux XUV and soft x-ray sources. Such sources are enabled by high harmonic generation with high average power femtosecond fiber lasers. Previous research included the demonstration of phase matching and efficient high harmonic generation at high repetition rates in the tight focusing regime [1], resonant enhancement of the macroscopic yield [2] and the demonstration of a high photon flux XUV source delivering more than 100 µW of average power per harmonic in the XUV [3]. In addition, high photon flux soft x-rays have been generated up to the carbon absorption edge located at 283 eV [4]. These unique table-top sources are employed for spectroscopy e.g. of highly-charged ion [5] and nanometer scale imaging [6].

spectrum nexafs

Measured optical density of a Parylene N filter
unveiling the fine structure of the carbon
absorption edge and contributions of different
binding orbitals (black points: raw data, red
curve: Fourier-filtered curve for better visibility).
diffraction pattern
Diffraction pattern of a nanoscale object
recorded with coherent XUV illumination.
The structure of this sample can be
reconstructed with record-high 13nm
spatial resolution.


[1] J. Rothhardt, M. Krebs, S. Hädrich, S. Demmler, J. Limpert, A. Tünnermann,
    "Absorption-limited and phase-matched high harmonic generation in the tight
     focusing regime," New J. Phys. 16, 033022 (2014).

[2] J. Rothhardt, S. Hädrich, S. Demmler, M. Krebs, S. Fritzsche, J. Limpert,
    A. Tünnermann,"Enhancing the Macroscopic Yield of Narrow-Band
    High-Order Harmonic Generation by Fano Resonances,"
    Phys. Rev. Lett. 112, 233002 (2014).

[3] S. Hädrich, A. Klenke, J. Rothhardt, M. Krebs, A. Hoffmann, O. Pronin,
    V. Pervak, J. Limpert, A. Tünnermann,"High photon flux table-top coherent
    extreme-ultraviolet source," Nat. Photon. 8, 779-783 (2014).

[4] J. Rothhardt, S. Hädrich, A. Klenke, S. Demmler, A. Hoffmann, T. Gotschall,
    T. Eidam, M. Krebs, J. Limpert, A. Tünnermann,"53 W average power few-cycle
    fiber laser system generating soft x rays up to the water window,"
   Opt. Lett. 39, 5224-7 (2014).

[5] J. Rothhardt, S. Hädrich, S. Demmler, M. Krebs, D. Winters, T. Kuehl, T. Stöhlker,
    J. Limpert, A. Tünnermann, "Prospects for laser spectroscopy of highly charged
   ions with high-harmonic XUV and soft x-ray sources," Phys. Scr. T166, 14030

[6] G. K. et al. Tadesse, "High Speed and High Resolution Table-Top Nanoscale
     Imaging," submitted (2016).

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