Ultrafast lasers and high-harmonic generation

  Ultrafast lasers and high-harmonic generation Copyright: © © Chair for Lasertechnology LLT, RWTH Aachen University. Nonlinear pulse compression in a multi-pass cell (MPC). The spectrum is broadened via SPM with every pass through a nonlinear element in the MPC. The simulated spectrum allows for pulse shortening by a factor of 9.


Dr. Johannes Weitenberg © Copyright: © private.


+49 241 80-40427


  Copyright: © © Chair for Lasertechnology LLT, RWTH Aachen University. Transverse mode profile (“slit mode“) in an enhancement resonator for high-harmonic generation (HHG). Measured beam profile in the HHG focus (top) and on the slit mirror (bottom) for geometrical output coupling of the EUV radiation.

Research focus

  • Generation/amplification and characterization of ultrashort pulses
  • Nonlinear compression of ultrashort pulses
  • High-harmonic generation (HHG) to the VUV and EUV spectral range
  • Resonator-assisted HHG at high repetition rates

Our group is engaged in ultrashort pulses (pulse duration in the femtosecond range) and their characterization, such as pulse duration, beam quality and homogeneity (spectrum across the beam profile). We work on nonlinear pulse compression in a multi-pass cell (MPC) and are aiming to study and extend the possible parameters for this scheme. For instance, a short pulse duration is important for high-harmonic generation (HHG) in a gas jet, because it yields weaker ionization and higher efficiency. HHG allows the generation of spatially and temporally coherent radiation in the vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) spectral range, producing odd harmonics of the driving radiation. For this highly nonlinear and inefficient process intensities <1e13 W/cm² are needed, which can be achieved by focusing of ultrashort pulses. A high repetition rates (>10 MHz) the radiation can be enhanced in a passive resonator to reach this intensity despite the limited pulse energy and to increase the overall efficiency. We are investigating different possibilities to geometrically couple the harmonics out of the resonator, without introducing large loss to the driving radiation. Coherent radiation in the VUV and EUV range at high repetition rate e.g. allows for frequency-comb spectroscopy in this spectral range or photoelectron spectroscopy with small disturbing space-charge effects.

Cooperation partner

  • Max-Planck Institute of Quantum Optics MPQ
  • Ludwig-Maximilians-Universität München LMU
  • Fraunhofer Institute for Laser Technology ILT


Together with Fraunhofer ILT, we are setting up a VUV frequency comb at 150 nm, which is generated as the 7th harmonic of a frequency comb at 1050 nm. The system will be installed at LMU Munich, where it will be used to optically excite an atomic nucleus (229Thorium) for the first time and to realize a nuclear clock. Such a clock has applications in fundamental physics, e.g. the search for dark matter [12]. The project is funded by the EU within an ERC Synergy Grant: https://thoriumclock.eu/

For students

Please contact us, if you are interested to work on our projects as a working student or within a Bachelor or Master thesis!


  1. P. Rußbüldt, J. Weitenberg, J. Schulte, R. Meyer, Ch. Meinhardt, H.-D. Hoffmann, R. Poprawe »Scalable 30 fs laser source with 530 W average power« Opt. Lett. 44, 5222-5225 (2019).
  2. T. Saule, S. Heinrich, J. Schötz, N. Lilienfein, M. Högner, O. deVries, M. Plötner, J. Weiten­berg, D. Esser, J. Schulte, P. Rußbüldt, J. Limpert, M. F. Kling, U. Kleineberg, I. Pupeza »High-flux, high-photon-energy ultrafast extreme-ultraviolet photoemission spectroscopy at 18.4 MHz pulse repetition rate« Nat. Comm. 10, 485 (2019).
  3. J. Weitenberg, T. Saule, J. Schulte, P. Rußbüldt »Nonlinear pulse compression to sub-40 fs at 4.5 µJ pulse energy by multi-pass-cell spectral broadening« IEEE JQE 53, 8600204 (2017).
  4. L. von der Wense, B. Seiferle, S. Stellmer, J. Weitenberg, G. Kazakov, A. Palffy, P. G. Thirolf »A laser excitation scheme for Th229m« Phys. Rev. Lett. 119, 132503 (2017).
  5. J. Weitenberg, A. Vernaleken, J. Schulte, A. Ozawa, Th. Sartorius, V. Pervak, H.-D. Hoffmann, Th. Udem, P. Rußbüldt, Th. W. Hänsch »Multi-pass-cell-based nonlinear pulse compression to 115 fs at 7.5 µJ pulse energy and 300 W average power« Opt. Express 25, 20502-20510 (2017).
  6. J. Schulte, Th. Sartorius, J. Weitenberg, A. Vernaleken, P. Rußbüldt »Nonlinear pulse com­pression in a multi-pass cell« Opt. Lett. 41, 4511-4514 (2016).
  7. J. Weitenberg, P. Rußbüldt, I. Pupeza, Th. Udem, H.-D. Hoffmann, R. Poprawe »Geometrical on-axis access to high-finesse resonators by quasi-imaging: a theoretical description« J. Opt. 17, 025609 (2015).
  8. P. Rußbüldt, D. Hoffmann, M. Höfer, J. Löhring, J. Luttmann, A. Meissner, J. Weitenberg, M. Traub, Th. Sartorius, D. Esser, R. Wester, P. Loosen, R. Poprawe »Innoslab amplifiers« IEEE J. Sel. Top. Quant. Electron. 21, 3100117 (2015).
  9. I. Pupeza, M. Högner, J. Weitenberg, S. Holzberger, D. Esser, T. Eidam, J. Limpert, A. Tünner­mann, E. Fill, V. S. Yakovlev »Cavity-enhanced high-harmonic generation with spatially tailored driving fields« Phys. Rev. Lett. 112, 103902 (2014).
  10. I. Pupeza, S. Holzberger, T. Eidam, H. Carstens, D. Esser, J. Weitenberg, P. Rußbüldt, J. Rauschenberger, J. Limpert, Th. Udem, A. Tünnermann, T. W. Hänsch, A. Apolonski, F. Krausz, E. Fill »Compact high-repetition-rate source of coherent 100 eV radiation« Nat. Phot. 7, 608-612 (2013).
  11. J. Weitenberg, P. Rußbüldt, T. Eidam, I. Pupeza »Transverse mode tailoring in a quasi-imaging high-finesse femtosecond enhancement cavity« Opt. Express 19, 9551-9561 (2011).
  12. E. Peik, T. Schumm, M. S. Safronova, A. Palffy, J. Weitenberg, P. G. Thirolf »Nuclear clocks for testing fundamental physics« Quantum Sci. Technol. 6, 034002 (2021).