DESY (Hamburg, Germany)

Laser development

• Ultrashort UV pulses: We generate ultrabroad ultraviolet pulses in the spectral range between 220 nm and 350 nm, reaching the record duration of sub-2 fs. Opt. Lett. 44, 1308-1311 (2019), J. Phys. Photonics 6, 025005 (2024).
• UV-IR or UV-XUV few-fs pump-probe setup: few-femtosecond UV pulses are synchronized to few-cycle near-infrared (NIR) and extreme ultraviolet (XUV) attosecond pulses. This setup allows for compactness while providing a long entrance arm for integrating different experimental chambers. The entire interferometer is built under vacuum to prevent both absorption of the XUV light and dispersion of the UV pulses, and it is actively stabilized to ensure an attosecond delay stability during experiments. Rev. Sci. Instrum. 95, 083004 (2024).
• Sub-cycle optical waveform synthesiser: Parametric waveform synthesis is used to generate phase-controlled sub-cycle waveforms at the millijoule energy level, with full-width at half-maximum durations down to 2.8 fs, that is, 0.6 optical cycles at a central wavelength of 1.4 μm. It enables the creation of extreme ultraviolet isolated attosecond pulses via high-harmonic generation without the need for additional gating techniques. The synthesized electric field is directly measured by attosecond-resolution sampling. Nature Photonics 14, 629–635 (2020).

Ultrafast electro dynamics in molecules

• Transient chirality: We use time-resolved photoelectron circular dichroism (TR-PECD) with an unprecedented temporal resolution of 2.9 fs to map the coherent electronic motion initiated by ultraviolet (UV) excitation of neutral chiral molecules. The combination of the photoinduced chiral current with a circularly polarized probe pulse realizes an enantioselective filter of molecular orientations following photoionization. We anticipate that our approach will enable further investigations of ultrafast electron dynamics in chiral systems and reveal a route towards enantiosensitive charge-directed reactivity. Nature 630, 109–115 (2024).
• Nanoplasmonics in fullerenes: Extreme light confinement in plasmonic nanosystems enables novel applications in photonics. We use attosecond photoemission chronoscopy to uncover the dominant role of electron correlations in the dynamics of the giant plasmon resonances (GPR) in fullerene molecules. Our approach provides novel insights into the nature of the plasmon resonances in subnanometer systems and open new perspectives for advancing nanoplasmonic applications.
• Charge migration: Sudden excitation or ionization of molecules can trigger a correlation-driven process called charge migration, where the electron density distribution rapidly changes. We use our ultrafast light sources to capture this few-femtosecond/attosecond charge redistribution in real time, offering important perspectives on controlling molecular reactivity at the electronic timescale. Commun Chem 4, 73 (2021).

We develop post-compressed and/or synthesized primary sources, with a particular emphasis on few-femtosecond, waveform-controlled infrared sources. Additionally, we design high-energy (100 mJ to 1 J) infrared sources for THz generation and high-average-power infrared frequency combs.

Our work also includes the realization of secondary sources ranging from THz pulses to few-femtosecond ultraviolet pulses. A key focus is on generating cutting-edge attosecond light sources through high-harmonic generation, producing photon energies that span from the extreme-ultraviolet to the soft X-ray spectral range.

These secondary sources are integrated into unique pump-probe setups, such as combining few-femtosecond UV pulses with attosecond XUV pulses, for ultrafast studies. Our research focuses on strong-field-driven phenomena, ultrafast atomic and molecular physics, and material science.

Laboratory 1: equipped with an attosecond beamline (STARLIGHT): this pump-probe setup is driven by sub-4fs NIR pulses (carrier wavelength 750 nm, bandwidth 400-1000 nm, 1.1-3.1 eV) obtained by hollow-core-fibre compression of a sub-20fs 10-mJ CEP-stable Ti:Sapph Laser operating at 1kHz repetition rate. It provides the unique availability of three different colors: 200-as nJ-level XUV pulses (photon energies in the range 15-50 eV), sub-2fs UV pulses (carrier wavelength 250 nm, bandwidth 210-340 nm, 3.6 – 5.9 eV) and sub-4fs NIR pulses. The uniqueness of this setup compared to other more conventional attosecond sources is the UV light source that delivers pulses short enough to explore the electron time scale in neutral molecules.

Laboratory 2: equipped with sub-cycle parametric optical waveform synthesizer that coherently combines carrier-envelope phase stable ~ 8 fs IR-pulses with up to 0.6 mJ with carrier-envelope phase stable ~ 8 fs near-IR OPA pulses with up to 0.1 mJ pulse energy to sub-cycle pulses with about 3 fs duration at a rep. rate 1 kHz. This system can be used for strong-field research and is also coupled to a HHG beamline to generate soft-X-ray isolated attosecond pulses up to 450 eV.

Laboratory 3: equipped with a 1 J, 300 ps at 1030 nm home-made laser system with the rep-rate 300 Hz for high-energy material science applications and THz generation.

Laboratory 4: equipped with a 100 mJ, 900 fs at 1020 nm home-made laser system with the rep. rate 1 kHz for high-energy material science applications and THz generation.

Laboratory 5: equipped with a high-average power IR frequency comb laser. This laser provides laser pulses of 200 fs duration at 1030 nm, an average power of 80 W and a repetition rate of 65 MHz. The comb system is CEP- and repetition rate stabilized providing CEP stable operation supporting >48 hours without CEP phase slips. The laser can be optionally post-compressed to < 40 fs pulse duration. In addition, the laser can be frequency-tuned covering a tuning range of 1000 nm – 1060 nm. Next to the laser system, a passive enhancement cavity is available supporting a passive intra-cavity power enhancement to an average power of multiple kW.