High Harmonic Generation (HHG)

High harmonic generation (HHG) is a laser-driven process which allows for creating extreme-UV and X-ray radiation while preserving the high quality of the laser beam. In our lab, we employ HHG as a source for lensless microscopy, where nanoscale images of investigated samples are retrieved from scattering diffraction signals via a computer algorithm, without the need for optical elements.

We employ a two-color generation scheme to control the polarization state of the emitted harmonics [Kfir et al., Appl. Phys. Lett. 108 (2016) ] and thus can investigate chiral systems or magnetic materials via x-ray magnetic circular dichroism (XMCD).

Recently, we demonstrated the first magnetic imaging using high-harmonic radiation [Kfir et al., 2017]. By employing an advanced detection scheme for weak scattering signals, we are currently reaching sub-20 nm spatial resolution, below the illuminating wavelength. Our combination of dichroic imaging with holographically-enhanced diffractive imaging allows us to extract the small dichroic signals independently from waveguiding effects in the sample [Zayko et al., 2016; Kfir et al., 2017]. With this approach, we reach spatial resolutions and image qualities competitive to those obtained at large-scale facilities such as synchrotrons, free-electron lasers for much shorter wavelengths.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 752533

Selected Publications

"Ultrafast high-harmonic nanoscopy of magnetization dynamics"  openaccess
S. Zayko, O. Kfir, M. Heigl, M. Lohmann, M. Sivis, M. Albrecht, C. Ropers
Nat. Commun. 12, 6337 (2021) [arXiv]

"Observation of fluctuation-mediated picosecond nucleation of a topological phase"
F. Büttner,, B. Pfau, M. Böttcher, M. Schneider, G. Mercurio, C. M. Günther, P. Hessing, C. Klose, A. Wittmann, K. Gerlinger, L.-M. Kern, C. Strüber, C. von Korff Schmising, J. Fuchs, D. Engel, A. Churikova, S. Hu
Nat. Mater. 20, 30-37 (2021)

"Chiral high-harmonic generation and spectroscopy on solid surfaces using polarization-tailored strong fields"  openaccess
T. Heinrich, M. Taucer, O. Kfir, P. B. Corkum, A. Staudte, C. Ropers and M. Sivis
Nat. Commun. 12, 3723 (2021) [arXiv]

 "Strong-field nano-optics"
P. Dombi, Z. Pápa, J. Vogelsang, S. V. Yalunin, M. Sivis, G. Herink, S. Schäfer, P. Groß, C. Ropers, and C. Lienau
Rev. Mod. Phys. 92, 025003-1 (2020)

"A dynamical symmetry triad in high-harmonic generation revealed by attosecond recollision control"  openaccess
S. Zayko, O. Kfir, E. Bordo, A. Fleischer, O. Cohen, C. Ropers
New J. Phys. 22, 053017 (2020)

"Interlocked attosecond pulse trains in slightly bi-elliptical high harmonic generation"  openaccess
E. Bordo, O. Kfir, S. Zayko, O. Neufeld, A. Fleischer, C. Ropers, O. Cohen
J. Phys. Photonics 2, 034005 (2020)

"Tailored semiconductors for high-harmonic optoelectronics"
M. Sivis, M. Taucer, G. Vampa, K. Johnston, A. Staudte, A. Y. Naumov, D. M. Villeneuve, C. Ropers, P. B. Corkum
Science 357, 303-306 (2017)

 "Nanoscale magnetic imaging using circularly polarized high-harmonic radiation"
O. Kfir, S. Zayko, C. Nolte, M. Sivis, M. Moeller, B. Hebler, S. S. P. K. Arekapudi, D. Steil, S. Schaefer, M. Albrecht, O. Cohen, S. Mathias, C. Ropers
Sci. Adv. 3, eaao4641 (2017) [arXiv]

"Polarization contrast of nanoscale waveguides in high harmonic imaging"  openaccess
S. Zayko, M. Sivis, S. Schaefer, C. Ropers
Optica 3, 239-242 (2016)

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