Center for Free-Electron Laser Science

We are a research group embedded in the Center for Free-Electron Laser Science (CFEL).

CFEL is a collaboration of Universität Hamburg, DESY, and the MPG to develop novel research programs to image structure and dynamics of matter and to utilize novel free-electron laser light sources.

The Hamburg Centre for Ultrafast Imaging (CUI)

We are strongly participating in the Hamburg Center for Ultrafast Imaging in research areas A and B.

This includes particularly the controlled particles imaging work with Henry Chapman's group, and joint projects with the laser physics group of Christian Kränkel and Günter Huber, which whom we develop a continuous laser for the control of molecules with strong ac electric fields, and with the group of Franz Kärtner with whom we work on characterizing novel coherent electron sources.

Quantum Dynamics in Tailored Intense Fields (QUTIF)

Laser-induced electron diffraction off strongly aligned and oriented molecules by tailored laser and DC electric fields

Within the QUTIF priority program and in collaboration with the group of Arnaud Rouzée from the Max Born Institute in Berlin we work on the imaging of complex polyatomic molecules using laser-induced electron diffraction. We prepare controlled samples using the electric deflector and laser-field-free alignment and mixed-field orientation with shaped laser pulses.


Light is our most important tool to observe and manipulate the microscopic world because the electromagnetic field of light waves exerts forces that we can control extremely well. When matter is exposed to light, it is the electrons that are immediately driven by these forces. Other degrees of freedom are then affected indirectly so that, for instance, chemical reactions can be triggered.

After several decades of laser development, we now witness the emerging capability to generate waveforms of light that are tailored at the level of the instantaneous electric field on a subfemtosecond time scale (1 femtosecond = 10-15 seconds) and with arbitrary polarization. Unlike the multi-cycle averaged effect of conventional laser pulses, these new waveforms can exert controlled instantaneous forces in arbitrary direction. The physics and chemistry of quantum systems in the presence of strong tailored light are the central theme of this Priority Programme. Typical laser intensities are in the range from 10 TW/cm2 to 1 PW/cm2 which means the applied field strength is comparable to the inner-atomic forces but mild enough to avoid immediate destruction of the target systems.

By tailoring fields with sub-cycle and sub-femtosecond precision to electronic and nuclear dynamics, they provide access to attosecond chemistry and physics (1 attosecond = 10-18 seconds). For example, attosecond pulses generated from strong-field interactions via high-harmonic generation can probe directly the temporal evolution of quantum systems with unprecedented speed. Photons, electrons and ions are emitted from irradiated systems and carry the information about microscopic dynamics. This information is often encoded in a non-obvious manner, requiring careful modelling of the underlying phenomena.

This six-year Priority Programme QUTIF is funded by the German Research Foundation DFG. It brings together physicists and chemists based in Germany to fully exploit the potential of the new laser sources. In this programme, we answer fundamental questions in atomic physics, we investigate molecular physics in strong controlled fields, we establish new applications in ultrafast chemistry, and we extend strong-field quantum dynamics to new media.

Molecular Electron Dynamics investigated by Intense Fields and Attosecond Pulses (MEDEA)

MEDEA is a Marie Skłodowska-Curie Innovative Training Networks (ITN-ETN) funded in the framework of the HORIZON 2020 program. The main objective of the MEDEA proposal is to create a platform where Early Stage Researchers will receive an inter-disciplinary and inter-sectoral comprehensive research training in one of the major field of Photonics that will be contributed by leading universities and research centers, and by key-player companies in the development and commercialization of state-of-the-art ultrafast laser sources and detection systems.

The interaction of matter with light is one of the most fundamental processes occurring in nature with countless scientific and technological applications. In recent years, the continuing development of intense, ultrashort, coherent light sources from the mid-infrared (mid-IR) to the extreme ultraviolet (XUV) spectral range has opened new possibilities for the investigation of this interaction in new and complementary domains. In both the IR and XUV regimes, molecules and clusters of atoms interacting with light exhibit (correlated) multi-electron dynamics evolving on the few femtosecond (1 fs=10-15 s) to attosecond (1 as=10-18 s) timescale. Several experimental and theoretical investigations suggest that ultrafast multielectronic processes might be fundamental in determining the behaviour of molecules and clusters, and that understanding these phenomena might offer new perspectives on processes occurring on “slower” timescales, such as bond-breaking in complex molecules and Coulomb explosion in charged clusters. In this context, the main objectives of the MEDEA network are: 1) to advance attosecond and femtosecond XUV spectroscopy in molecules and clusters 2) to demonstrate the feasibility of nonlinear attosecond XUV spectroscopy, 3) to obtain benchmarks for the validation of attosecond tools and femtosecond XUV pulses for the time-resolved imaging of electron and nuclear dynamics in molecules, 4) to contribute to the development of new technological solutions that will increase the competiveness of the industrial partners 5) to train a group of early stage researchers (ESRs) and contribute to their career prospects, and 6) to increase the interest of young students in the network’s core research field (Photonics) by introducing a dedicated experimental kit in several European secondary schools.

Well-designed activities will be offered by the network to enhance the Early Stage Reseachers’ career perspectives in both the academic and private sector, with a particular attention to high-quality training in research, innovation, management and entrepreneurship as well as communication skills.

Through their research activities Early Stage Reseachers will contribute to the advance of attosecond and intense femtosecond extreme ultraviolet spectroscopy combining in-depth investigation of fundamental electronic processes in simple systems with experiments in complex molecules with potential impact in chemistry, surface science, and biology.

See the project's website for more information.

Angular studies of photoelectrons in innovative research environments (ASPIRE)

In the ASPIRE project, whose academic and industrial beneficiaries are world leading in their complementary fields of expertise, the overarching research goal is the measurement of photoelectron angular distributions (PADs) in the “molecular frame” (MF) of systems of biological relevance. These MF-PADs can be interpreted as electron diffraction patterns, achieved by “illuminating the molecule from within”, and enable the shapes and motions of individual molecules to be interrogated. Such knowledge is needed for the development of new medicines (the shapes of drug molecules dictate their function) and new materials (efficient solar cells can be constructed if energy dissipation processes in molecules are understood). Progress in this area is highly technologically driven, requiring high repetition rate, short wavelength light sources and fast detectors. The input of private sector beneficiaries is therefore critical to the scientific objectives, as well as to the enhanced training environment. Work packages on advanced light source and detector developments will feed into the overall goal through secondments, regular virtual meetings and face-to-face network meetings. The symbiosis of the developments that will take place in ASPIRE will create a research and training environment that is world-leading and optimally tailored to capitalise, for example, on the investment that has been made in the European XFEL facility. The ESRs will be trained in world-leading laboratories and will benefit from the exchange of best practice among beneficiaries and partners, and from unique training events. ASPIRE will therefore ensure that European research remains competitive in the global market, and that the trained researchers will be uniquely well-placed to contribute to the development of novel instrumentation in the future.

International Max Planck Research Schools (IMPRS-UFAST)

We are participating in the International Max Planck Research School for Ultrafast Imaging and Structural Dynamics (IMPRS-UFAST) graduate school through student supervision and teaching.

Helmholtz Virtual Institute "Dynamic Pathways in Multidimensional Landscapes"

We are collaborating in the Helmholtz Virtual Institute "Dynamic Pathways in Multidimensional Landscapes", esp. through the supervision of Project P1 "Ultrafast isomerization dynamics of conformer-selected aligned gas-phase molecules".

The Virtual Institute explores the governing principles of material’s function in an internationally highly visible centre of excellence, where through a series of interdependent investigations researchers from HZB and DESY and two German Universities join forces with the Virtual Institute’s national and international associated partners. Scientifically, we gain a unifying view on material classes whose properties are governed by coupled internal degrees of freedom (charge, orbit, spin, and nuclear motion) that interact with the environment (external fields and heat baths). These properties lead to functionality we can utilize and tailor to harvest and store energy, communicate and archive knowledge. Since low energy excitations, nanoscale order and ultra fast timescales are involved, we propose to engage in a science program along these three dimensions of energy, space and time. Thus, we intentionally cross the boundaries between solid, liquid and molecular systems.

Ultrafast isomerization dynamics of conformer-selected aligned gas-phase molecules

Complex molecules exhibit multiple conformers (structural isomers), even under the cold conditions (~1 K) of a molecular beam. Since the first observation of multiple conformers in the 1980s – for the essential amino acid tryptophan (C11H12N2O2) – the structures of conformers of many molecules have been investigated using advanced spectroscopic techniques. However, while a lot of data on the local minima on the global energy landscape has been collected, little is known on the connecting valleys and transition states on the potential energy landscape, mainly because ultrafast dynamics experiments would average over the effects for the various conformers present in the sample. Moreover, due to the complexity of these molecules, there is usually not enough prior knowledge to unravel the details of (UV/VIS) spectroscopic pump-probe experiments. We have developed methods to spatially separate structural isomers of neutral molecules, using inhomogeneous electric fields, according to their electric dipole moment to mass ratio. These methods are quantum-state selective and very polar samples are created. This allows us to strongly align and orient these samples. We also separate the molecules from the atomic seed gas, avoiding background signals from the atoms which often obscure the molecular signals.

The goal of this project is to create strongly 3D-aligned and oriented samples of individual conformers in order to investigate their ultrafast inter-conversion dynamics using coherent X-ray diffractive imaging, time-resolved X-ray spectroscopy, and X-ray-induced molecular-frame photoelectron angular distributions. Moreover, these complex molecules with many structural isomers are also prototypical versatile molecular switches. A detailed screening of various molecular systems could open new avenues toward applicable molecular switches and especially toward multi-state switches – corresponding to molecules with multiple (> 2) accessible structural isomers.


The aim of this project is to elucidate the intrinsic inter-conversion dynamics of controlled complex molecules.


Within this project the same class of molecules/same molecule will be investigated as in projects P2 and P3. Experiments will be performed at partner institutes, such as spectroscopy for electronic structure information with high-order harmonic photon source at HZB/MBI; molecular-frame photoelectron-angular distributions with synchrotron source (Petra III/BESSY II) and HHG sources (MBI). Complementary information on the geometric structure will be gained in the gas phase (this project) and on the electronic structure (P2, P3) and influence of environments (this project, P2, P3). There will be theoretical support from P10 and methodological synergy with P4, P5 and P8.

Laser alignment and mixed-field orientation (Hamburg–Aarhus–Granada)

We are investigating the alignment and orientation of large, state selected molecular samples in collaboration with the group of Henrik Stapelfeldt at the University of Aarhus, Denmark and with Rosario González Férez at the Universidad de Granada, Spain. In this collaboration we have successfully coupled the state selection, due to the dc Stark effect, and rotational alignment and orientation, due to the ac Stark effect, in order to obtain unprecedented degrees of alignment and mixed-field orientation. We have developed a detailed experimental and theoretical understanding of the rotational motion of molecules in electric fields.

Reaction kinetics (Hamburg–Basel)

Investigations of conformer-specific chemical reactivities are performed with the group of Stefan Willitsch (University of Basle, Switzerland).

Optically Controlled Particles (Hamburg–Canberra)

The manipulation of large (100 nm to 10 μm sized) samples using designed laser beams is performed in collaboration with Henry Chapman (CFEL) and Andrei Rode and Niko Eckerskorn from Australian National University (Canberra, Australia).

X-FEL investigations of gas-phase molecules

Our projects on the diffractive imaging and photoelectron investigations of controlled gas-phase molecules are performed in collaboration with the Coherent Imaging Division (Henry Chapman), colleagues from the former Max-Planck Advanced Study Group at CFEL (e.g., Daniel Rolles, DESY; Artem Rudenko, Kansas State University), the groups of Henrik Stapelfeldt (Aarhus University), Arnaud Rouzee and Marc Vrakking (Max-Born-Institute Berlin), and many other colleagues around the world.