Synthesis of optical waveforms promises a "brighter" future for attosecond science

Custom-tailored waveforms and pulse length

Attosecond streaking

Attosecond streaking and extracted waveform. Measured attosecond streaking trace of the synthesised waveform, acquired with 200 as delay step size over 10 minutes (Credit: Original Publication in Nature Photonics).

Optical scheme

Optical scheme of the parametric waveform synthesiser (Credit: Original Publication; slightly changed colours)

An international team with scientists from DESY, Massachusetts Institute of Technology (MIT Boston, US), Politecnico di Milano (Italy) and Universität Hamburg, has synthesised ultrashort and intense flashes of light, so-called "optical waveforms". Their duration of a few attoseconds (as) is less than the time required by the light wave to complete a single oscillation cycle. Moreover, the optical waveforms with non-sinusoidal shape can be tailored in the generation process. These achievements in ultrafast laser technology are paving the way to customisable light flashes in the whole optical range and will enable novel experiments in the attosecond regime. All findings were published in the journal Nature Photonics.

The particular approach to "sub-cycle" waveform synthesis pursued here relies on a process called "optical parametric amplification" which allows to generate ultrashort laser pulses tunable from the ultraviolet (UV) to the mid-infrared (mid-IR) spectral region. Moreover, the parametric amplification can be cascaded to achieve even higher pulse energies. Therefore, the applied parametric synthesis appears to be the most promising approach to the generation of sub-cycle optical waveforms with scalable bandwidth energy and average power.

"Synthesised optical waveforms are expected to bring tremendous advantages in the control of strong-field light-matter interactions. In this case the electromagnetic field of light is strong enough to counteract the forces that bind electrons and nuclei and to drive the released electrons along a particular trajectory", explains Giulio Maria Rossi, scientist at DESY and the Universität Hamburg.  "We have shown that sub-cycle optical waveforms can be used to directly generate isolated attosecond pulses, probably the shortest events that human technology can currently create via the strong-field high-harmonic generation (HHG) process."

The possibility to shape the electric field is expected to allow overcoming limitations in terms of conversion efficiency and cut-off extension intrinsic to the HHG process, therefore enabling brighter attosecond pulses reaching up to higher photon energies. Moreover, by controlling the electron trajectories, it will also be possible to control the central energy in a continuous way, as well as the bandwidth and the chirp of the attosecond pulses. These discoveries are expected to further advance attosecond science by making it easier to conduct attosecond measurements, e.g. in the 'water window' soft X-ray region.

"The parametric waveform synthesis can be transferred to different pump laser technologies allowing to reach much higher energies and average powers compared to what we demonstrated here", adds Franz Kärtner, lead scientist at DESY and professor at the Universität Hamburg. “This could allow exploring the impact of custom-tailored waveforms on relativistic strong-filed processes such as laser-plasma wakefield acceleration.”


ReferenceSub-cycle mJ-level Parametric Waveform Synthesizer for Attosecond Science; G. M. Rossi, R. E. Mainz, Y. Yang, F. Scheiba, M. A. Silva-Toledo, S.-H. Chia, P. D. Keathley, S. Fang, O. D. Mücke, C. Manzoni, G. Cerullo, G. Cirmi, and F. X. Kärtner, Nature Photonics (2020), DOI: 10.1038/s41566-020-0659-0.


The research project was supported by DESY and the Helmholtz Association (HGF), by the Cluster of Excellence ‘CUI: Advanced Imaging of Matter’ of the Deutsche Forschungsgemeinschaft (DFG)-EXC 2056-project ID 390715994, by the priority programme ‘Quantum Dynamics in Tailored Intense Fields’ (QUTIF) (SPP1840 SOLSTICE) of the DFG, by the European Research Council (ERC) with the Synergy Grant  ‘Frontiers in Attosecond X-ray Science: Imaging and Spectroscopy’ (AXSIS; further info: 'Results in brief'), and by the MIT-Hamburg Research Network through the Behörde für Wissenschaft, Forschung und Gleichstellung in Hamburg.