Advances in photonics and laser physics render possible the generation of electromagnetic fields with spatio-temporally shaped phase and polarization states, both in the near and far field. The talk addresses the distinctive features of the interaction of matter with optical vortices, vector fields, and optical skyrmions. Emphasis is put on the strongly non-linear, spin-dependent quantum dynamics and the consequences of geometry and topology of the driving fields on the generated charge and spin densities and currents. The potential of polarization and phase engineering of the light wave for fundamental and applied research is illustrated by examples from condensed matter and atomic physics.

Akademischen Festvortrag zur Verleihung der Ehrendoktorwürde der Mathematisch-Naturwissenschaftliche Fakultät der Universität Rostock an Professor Dr. Paul B. Corkum.

I will describe a new technique of chiral recognition, based on the excitation of coherent helical motion of bound electrons in valence shells of a chiral molecule [1]. Unlike the helix of light, traditionally used for chiral recognition in neutral molecules, the helical motion of the electrons has the right size to explore molecular chirality, leading to strong ultrafast chiral response.

The most established technique of probing chiral interactions, the photoabsorption circular dichroism, relies on interaction with circularly polarized light. Distinguishing right-handed from lefthanded molecules relies on the molecule sensing the chiral nature of the circular light. The helix of the light-wave is given by its wavelength. Hence, for optical fields, it exceeds the size of the molecule by several orders of magnitude. As a consequence, the related chiral effect – the photoabsorption circular dichroism – is very small. Formally, to feel the pitch of the lightwave, one needs to look be-yond the dipole approximation, relying on the magnetic component of the laser field. Small value of the chiral signal makes ultrafast measurements of chiral dynamics very challenging.

One possible way of increasing chiral response is to avoid the reliance on magnetic field effects and therefore perform chiral measurements without chiral light. We describe the concept underlying such measurements. We present a unified description of several methods of chiral discrimination based on electric-dipole interactions. We show that, in spite of the fact that the physics underlying the appearance of a chiral response is very different in all these methods, the chiral observable in all cases has a unique form. It is a polar vector given by the product of (i) the molecular pseudoscalar and (ii) the field pseudovector specified by configurations of the electromagnetic fields interacting with an isotropic ensemble of chiral molecules. The molecular pseudoscalar is a rotationally invariant property, which is composed from different moleculespecific vectors and in the simplest case is a triple product of such vectors. The key property that enables the chiral response is the non-coplanarity of the vectors forming such triple product. The key property that enables chiral detection without using chiral electromagnetic fields is the vectorial nature of the enantio-sensitive observable.

Finally, we will discuss geometrical and topological origins of chiral response. Handedness is a purely geometrical degree of freedom. In analogy with solids, where geometry and topology play important role in electronic response, we show that one can introduce chiral fields and chiral charges of geometrical origin that drive one-photon chiral response.

[1] S. Beaulieu, et al. "Photoexcitation Circular Dichroism in Chiral Molecules", Nature Physics, 2018

For more than 100 years, X-rays have been used to determine the structure of crystals and molecules via coherent diffraction methods. These techniques rely on coherent scattering where incoherence due to wavefront distortions or incoherent fluorescence emission is considered as detrimental. Here we show that methods from quantum imaging, i.e., exploiting higher order intensity correlations, can be used to image the arrangement of sources that scatter incoherent X-ray radiation [1-5]. We present this new Incoherent Diffraction Imaging (IDI) method and discuss a number of properties that are conceptually superior to those of conventional coherent X-ray structure determination [4]. We also report an experimental demonstration in the soft x-ray domain, where higher-order intensity correlations are used to achieve higher fidelities in the image reconstruction and potentially a sub-Abbe resolution [5], and discuss recent experiments aiming at full 3D reconstruction of different samples with atomic resolution using hard x-rays.

[1] C. Thiel, T. Bastin, J. Martin, E. Solano, J. von Zanthier, G. S. Agarwal, Phys. Rev. Lett. 99, 133603 (2007)
[2] S. Oppel, T. Büttner, P. Kok, J. von Zanthier, Phys. Rev. Lett. 109, 233603 (2012)
[3] A. Classen, F. Waldmann, S. Giebel, R. Schneider, D Bhatti, T. Mehringer, J. von Zanthier, Phys. Rev. Lett. 117, 253601 (2016)
[4] A. Classen, K. Ayyer, H. N. Chapman, R. Röhlsberger, J. von Zanthier, Phys. Rev. Lett. 119, 053401 (2017)
[5] Schneider et al., Nature Physics 14, 126 (2018); News and Views, Nature Photonics 12, 6 (2018)

Recent developments exploring a new regime of quantum physics will be presented, where subcycle and sub-wavelength confinement in both time and space opens up access to new phenomena owing to the absence of local conservation of energy and momentum.

The first part features subcycle quantum physics of the electromagnetic field. Reading out the nonlinear displacement of valence electrons in a semiconductor with few-femtosecond laser pulses allows direct sampling of vacuum fluctuations [1,2]. Synchronal noise patterns of squeezed mid-infrared transients are generated and characterized as a first application of this new type of quantum technology [3]. Local deviations from the vacuum noise level arise due to acceleration of the reference frame combined with Heisenberg’s uncertainty principle.

Latest progress in attosecond control of nanotransport in the few-electron range [4] will be presented in the second part. Here, we use single cycles of near-infrared radiation from a passively phase-locked Er:fiber system to direct the current between two nanometer-sized contacts made up by a plasmonic antenna. This combination addresses extremely nonlinear optics with pulses of minute energy content in the pJ range. At the moment, we are working towards truly atomic spatio-temporal dimensions where novel quantum transport processes like dynamical Coulomb blockade might prevail.

[1] C. Riek et al., Science 350, 420 (2015)
[2] A. S. Moskalenko et al., Phys. Rev. Lett. 115, 263601 (2015)
[3] C. Riek et al., Nature 541, 376 (2017)
[4] T. Rybka et al., Nature Photon. 10, 667 (2016)

Observing electron dynamics in matter on its natural time scale requires attosecond technology. I will show how isolated attosecond pulses can be used in combination with phase-stable infrared/ ultraviolet pulses to track ultrafast charge dynamics in biorelevant molecules such as aromatic amino acids. These scheme can be also used to investigate the ultrafast mechanisms behind the photo stability of our own DNA. Our results open new important perspectives for a future understanding of the role of the electronic motion in the photochemistry and photobiology of complex molecules.

My group at the Chair for Medical Physics at the LMU Munich investigates the acceleration of ion bunches trough the interaction of laser pulses at relativistic intensities with plasmas. Over the last 15 years, Laser-ION (LION) acceleration has been the focus of intense research, which I will review in my talk. Our main objective is to realise viable sources for applications in radiation physics, chemistry, biology and medicine. Currently, we establish the Centre for Advanced Laser Applications (CALA), which will feature a laser system able to provide 20 fs short laser pulses with peak power of up to 3 Peta-Watt.

This talk will provide information on the ultrafast processes that lead to the acceleration of ions to kinetic energies from a few to 10s of MeV per nucleon. I will highlight the challenges and limits of our current understanding to provide a basis for fruitful discussions. Those difficulties mainly originate from the fact that in the focus of a PWlaser pulse, the light intensities rise from the damage threshold of solid matter (~10¹³ W/cm²) via relativistic intensities (10¹⁸ W/cm²) to the maximum intensity (10²⁰…10²² W/cm²) within a few 10s of picoseconds, while the actual acceleration phase in electric fields of the order MV/µm happens within a few 10s of femtoseconds only.

Rydberg atoms have enormous electric dipole moments, and, due to their dipoledipole interactions, a frozen Rydberg gas resembles a solid. Two important difference are that the density is thirteen orders of magnitude lower and that its properties are easily manipulated using static and microwave fields. After a brief summary of the important properties of Rydberg atoms, examples of exciton like energy transfer will be presented. In particular, experiments demonstrating Forster energy transfer brought into resonance with static fields and microwave transitions of pairs of atoms will be described. While the two types of experiments are apparently very different, the latter can be thought of as Forster resonant energy transfer between microwave dressed states.

The particle emission by a sub-micron spherical solid target, when irradiated from a two-cycle laser pulse with 1 micron focus, has been studied in detail with 2D and 3D PIC simulations and modeled according to [1]. In order to get a deeper insight about the physics of the process, the results for an isolated cluster sphere in the laser focus have been further compared with 3D simulations for a needle owing a spherical tip with same size. The dynamics of the electron emission has been investigated mostly numerically, following the general intuition that existing theory already tested for gaseous droplets and non relativistic laser intensity [2] would be replaced to a good approximation by nonlinear scattering at the laser focus. It has been shown that the attosecond bunch emission process still holds and the emitted particle orientation only depends on the shape and dimension of the target with respect to the criteria and parametric curve defined in [1].

[1] L. Di Lucchio, P. Gibbon, “Relativistic attosecond electron bunch emission from few-cycle laser irradiated nanoscale droplets”, Phys. Rev. ST Accel. Beams 18, 023402 (2015)
[2] T. V. Liseykina, S. Pirner, and D. Bauer, “Relativistic attosecond electron bunches from laserilluminated droplets”, Phys. Rev. Lett. 104, 095002 (2010)

The spatial confinement of light using metallic nanostructures enables the enhancement of a multitude of different nonlinear optical phenomena, including harmonic generation, atomic ionization, and nonlinear photoemission. This talk will discuss the nonlinear and field-driven interaction of electrons with localized optical near-fields at nanostructures over a broad range of physical parameters, with an emphasis on several examples of our recent and ongoing work. Specifically, we study the characteristics of ultrafast photoelectron emission from nanoscopic cathodes, and develop strategies to control this photoemission for applications in time-resolved electron imaging and diffraction.

In one set of measurements, photoemission spectra from electrochemically etched metal nanotips are investigated and controlled using intense near- and mid-infrared laser pulses, as well as THz radiation. In an application of nanotip photoemission, the enhanced brightness of these electron sources is used to implement Ultrafast Low-Energy Electron Diffraction (ULEED) and Ultrafast Transmission Electron Microscopy (UTEM). UTEM allows for the study of quantum features in the interaction of free electrons with optical near-fields. We demonstrate coherent manipulations of the longitudinal and transverse momentum distributions, which facilitates the production of attosecond electron pulse trains.

[1] M. Sivis, M. Duwe, B. Abel and C. Ropers, "Extreme-ultraviolet light generation in plasmonic nanostructures", Nature Physics 9, 304(2013)
[2] M. Sivis and C. Ropers, "Generation and Bistability of a Waveguide Nanoplasma Observed by Enhanced Extreme-Ultraviolet Fluorescence", Phys. Rev. Lett. 111, 085001 (2013)
[3] R. Bormann, M. Gulde, A. Weismann, S. V. Yalunin, and C. Ropers, "Tip-enhanced strong-field photoemission" Phys. Rev. Lett., 105, 147601 (2010)
[4] G. Herink, D. R. Solli, M. Gulde, and C. Ropers, "Field-driven photoemission from nanostructures quenches the quiver motion", Nature 483, 190 (2012)
[5] L. Wimmer, G. Herink, D. R. Solli, S. V. Yalunin, K. E. Echternkamp, and C. Ropers, "Terahertz control of nanotip photoemission", Nature Physics 10, 432 (2014)
[6] A. Paarmann, M. Gulde, M. Müller, S. Schäfer, S. Schweda, M. Maiti, C. Xu, T. Hohage, F. Schenk, C. Ropers and R. Ernstorfer, "Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study", Journal of Applied Physics 112, 113109 (2012)
[7] M. Gulde, S. Schweda, G. Storeck, M. Maiti, H. K. Yu, A. M. Wodtke, S. Schäfer, and C. Ropers, "Ultrafast low-energy electron diffraction in transmission resolves polymer/graphene superstructure dynamics", Science 345, 200 (2014)
[8] A. Feist, K. E. Echternkamp, J. Schauss, S. V. Yalunin, S. Schäfer, and C. Ropers, "Quantum coherent optical phase modulation in an ultrafast transmission electron microscope", Nature 521, 200-203 (2015)

Light scattering by small particles is widely used in remote sensing of various objects ranging from metal nanoparticles and macromolecules to atmospheric aerosols and interstellar dust, being in some cases the only available approach to characterize their geometric or optical properties. Moreover, the structure of electromagnetic near-fields of particles is also of major importance for other phenomena, such as surface-enhanced Raman scattering or electron-energyloss spectroscopy. All these applications require accurate light-scattering simulations, which is not trivial for particles of arbitrary shape and internal structure with sizes comparable to or larger than the wavelength. The discrete dipole approximation (DDA) is one of the general methods to handle such problems and nowadays is freely available in mature parallelized open-source codes. In this talk, I will provide a short introduction to this method, including both the underlying physics and important computational aspects, and will describe two of the recent developments of the DDA. The first addresses the rigorous and fast description of particles near the plane substrate as realized in essentially all scenarios using deposited particles. While the configuration is very common in many applications (especially nanoparticles), all previous implementations were much slower than the free-space DDA, motivating the practitioners to either ignore the substrate or use some hard-to-control approximations. The second development is the DDA with rectangular cuboid dipoles (volume discretization elements). Such formulation is relevant for very oblate or prolate particles with at least one dimension much smaller than the wavelength, e.g. a graphene sheet.

The advent of laser-driven ultrafast sources based on high harmonic generation (HHG) spanning the extreme ultraviolet (XUV) into the soft X-ray regime offer magnificent opportunities for time-resolved research. Their short wavelength and excellent coherence properties enable microscopy applications at the nanoscale and at shortest timescale. Tremendous progress has been made towards better resolution and shorter exposure times since the first demonstration of employing a HHG source for coherent diffraction imaging in 2008. In this talk recent developments towards reaching 10 nm spatial resolution with a table-top instrument using coherent diffraction imaging will be presented [1]. One strength of coherent imaging techniques is resolving the object under test in amplitude and phase, which automatically incorporates known visible light imaging regimes, such as phase contrast or dark-field microscopy. The high resolution and contrast achieved can for instance be applied for imaging unlabeled specimen in reflection geometry [2] allowing for classifying breast cancer cells diffraction pattern analysis [3]. Another strength of high harmonics is the ultimate time resolution down to about a hundred attoseconds due to the large bandwidth in the XUV. Time-resolved spectroscopy using HHG allows element, oxidation state and charge specific investigations and as such has the ability to unravel complex charge dominated processes at shortest time scales. Recent progress on time domain spectroscopy on charge dynamics in semiconductors will be presented [4], revealing electron and hole dynamics at unprecedented temporal resolution [5]. Finally, prospects of the field towards two-dimensional attosecond spectroscopy in highly anisotropic materials and bio-relevant molecules along with latest experimental developments will be discussed.

[1] M. Zürch, et al., Nature Scientific Reports 4 (7356), 1-5 (2014)
[2] M. Zürch, et al., Optics Express 21 (18), 21131-21147 (2013)
[3] M. Zürch, et al., Journal of Medical Imaging 1 (3), 031008 (2014)
[4] L. J. Borja, M. Zürch, et al., Journal of the Optical Society of America B 33 (7), C57-C64 (2016)
[5] M. Zürch, et al., International Conference on Ultrafast Phenomena, New Mexico, July 18th 2016

Having the shortest optical [1-3] and soft x-ray fields [4] as a part of its repertoire, attosecond physics has recently opened up new avenues for exploring ultrafast electronic processes in atoms [5,6] , molecules [7], surfaces [8] and nanostructures [9]. I will discuss how modern advancements of the “ultrafast toolbox” allow for the first time, the exploration and control of fundamental electronic phenomena in condensed media. Electron motion in bulk media, driven by intense, precisely-sculpted, optical fields give rise to controllable electric currents, the frequency of which extends to the multi-Petahertz range [9-10], advancing lightwave electronics [10] to new realms of speed and precision. Coherent extreme ultraviolet radiation emerging by these coherent charge oscillations [9] offers direct insight into structural and dynamical properties of the underlying medium which were previously inaccessible to conventional solid-state spectroscopies. By endowing essential x-ray spectroscopies of solids with attosecond temporal resolution, optical half-cycle fields, combined with extreme ultraviolet pulses, offer for the first time, access into the attosecond dephasing of electronic excitation of highly-correlated condensed phase electronic systems [11]. We anticipate these new capabilities to result in far reaching implications to fundamental and applied, electronic and photonic sciences.

[1] Goulielmakis E. et al., Science 305, 1267 (2004)
[2] Wirth A. et al., Science 334, 195 (2011)
[3] Hassan M. Th et al., Nature 530, 66 ( 2016)
[4] Goulielmakis E.et al., Science 320, 1614 (2008)
[5] Goulielmakis E. et al., Nature 466, 739 (2010)
[6] Kienberger R. et al., Nature 427, 817 (2004), Smirnova et. al, Nature 460, 972 (2009)
[7] Cavalieri A L et al., Nature 449, 1029 (2007)
[8] Krueger M et al. Nature 475, 78 (2011)
[9] Luu T.T. et al., Nature 521, 498 (2015), Garg el., Submitted (2015)
[10] Goulielmakis E. et al., Science 317, 769 (2007)
[11] Moulet A. et al., in preparation (2016)

The spatial migration of an electron hole following excitation or ionization is a fundamental process in nature and engineering. Charge migration controls the regioselectivity of chemical reactions, energy transport in biological systems and underlies molecular electronics.

In this talk, I will discuss the experimental investigation of charge migration in a molecular cation on the attosecond time scale. High-harmonic spectroscopy (HHS) has been developed further to perform a direct reconstruction of time-dependent populations and phases of electronic eigenstates with a resolution of 70-130 as. The reconstruction employs measured amplitudes and phases of the high-harmonic emission from oriented molecules at multiple wavelengths of the driving field.

We demonstrate this technique using iodoacetylene (ICCH) as an example. We use control over the spatial orientation of the molecule [1-3] to separate field-free from laser-controlled charge migration. For molecules aligned perpendicular to the laser polarization, charge migration takes place under conditions similar to the absence of an external field. In particular, we determine the shape of the hole created by strong-field ionization and its subsequent time evolution. We further demonstrate extensive laser control over charge migration by orienting the molecules parallel or anti-parallel to the laser polarization. The laser-controlled charge migration fundamentally differs from the field-free process. We find significant population transfer between the two lowest field-free electronic eigenstates for both investigated wavelengths (800 nm and 1300 nm). The population transfer furthermore strongly depends on the head-to-tail orientation of the molecules.

[1] P. M. Kraus, A. Rupenyan, H. J. Wörner, Phys. Rev. Lett. 109, 233903 (2012)
[2] P. M. Kraus, D. Baykusheva, H. J. Wörner, Phys. Rev. Lett. 113, 023001 (2014)
[3] P. M. Kraus et al., Nat. Commun. 6, 7039 (2015)

The generation of coherent brilliant attosecond radiation is of great interest for spatio-temporal investigations of the structure of matter. Radiation from the interaction of infrared lasers with atoms can be in the attosecond domain. However, it is generally impossible to obtain attosecond hard x-rays from the interaction of such laser radiation with atoms. More recently there was experimental evidence that high harmonics of the laser fundamental can be generated by an oscillating plasma mirror created during the interaction of intense infrared laser radiation with solid targets. The interaction of an intense, few-cycle laser pulse in the infrared with a nanometer thick solid density foil is investigated in one dimension (1D). A simple analytical model is discussed. It is shown that at a certain intensity threshold most electrons leave the nano-foil and create a strong space-charge field. Under certain conditions a dense ultra-relativistic electron mirror can be created that can up shift the frequency of the incoming infrared radiation. It is shown that simulation and analytical model agree with each other provided the foil is assumed to be rigid in the simulation and the numerical resolution is sufficiently high. At ultra-high laser intensity radiation friction is expected to be dominating. Radiation friction can lead to trapping of radiating electrons in specific ultra-intense field configurations. The effect is discussed.

The accessibility of few femtosecond or even attoseconds pulses opens the door to direct observation of electron dynamics. The idea to steer chemical reactions by localization of electronic wavepackets is intriguing, since electrons are directly involved in bond breaking and formation. The formation of a localized electronic wavepacket requires the superposition of two or more appropriate electronic states. Its guidance is only possible within the coherence time of the system and has to be synchronized with the vibrational molecular motions. In theoretical studies we elucidate the role of electron wavepacket motion for the control of molecular processes. We give three examples with direct connection to experiments. From our analysis, we extract the systems requirements defining the time window for intramolecular electronic coherence, the basis for efficient control. Based on these findings we map out a photoreaction that allows direct control by guiding electronic wavepackets. The carrier envelope of a femtosecond few cycle IR pulse is the control parameter that steers the photoreaction through a conical intersection.

Atomic clusters were among the first targets in upcoming Xray free-electrons lasers. Rather then just bridging the gap between point-like atoms and extended solids they possess unique properties which do not appear in either of the limiting cases. Albeit the interaction with short-wavelength radiation occurs locally with core electrons the high atomic density in finite systems, like clusters, has profound consequences. I will discuss some of them, e.g. the formation of novel nano-plasmas, massively parallel ionization, energy bunching in Coulomb explosion or the dynamical segregation in molecular systems. Although the dynamics is a complicated many-particle process it can sometimes be described by simple analytical models.

Die Wechselwirkung von Licht mit lokalisierten Plasmonen (LSPs) und OberflächenPlasmon-Polaritonen (SPPs) eröffnet einen Weg um Licht in elektrische Signale (und zurück) zu konvertieren - ohne dafür aufwendige elektronische Detektoren und Schaltkreise aufbauen zu müssen. Diese vielversprechende Möglichkeit hat eine ganze Forschungsrichtung inspiriert, die sich damit beschäftigt plasmonische Anregungen durch Licht zu erzeugen, nano-optische Funktionalität auf Basis von Plasmonen auf Größenskalen unterhalb des Beugungslimits zu realisieren, und letztendlich die plasmonische Anregung wieder in das optische Fernfeld zu koppeln. In den vergangenen Jahren wurde für die Untersuchung von Oberflächen-PlasmonPolaritonenwellen verstärkt die Methode der nichtlinearen Photoelektronenmikroskopie verwendet. Hier wird in einem Elektronenmikroskop mittels eines Photons aus einem Laserpuls eine Plasmonenwelle gestartet (Anregung), aus der dann mittels eines weiteren Photons (Abfrage) ein Photoelektron extrahiert werden kann. Dieses zweite Photon kann entweder aus dem anregenden oder abfragenden Laserpuls stammen, oder auch durch das plasmonische Feld selber zur Verfügung gestellt werden. In zeitaufgelösten Experimenten unter ‘senkrechter Beleuchtung’ der Probe mit femtosekunden Laserpulsen ist es so möglich, die zeitliche Dynamik von propagierenden SPPs abzubilden und Details der Wechselwirkung von Plasmonenwellen miteinander zu untersuchen.

COLTRIMS Reaction Microscopes today allow measuring the correlations between all fragments (electrons and ions) from ionization processes of atoms and molecules. We will show synchroton, laser and ion beam based experiments, where this technique is used to explore fundamental quantum phenomena such as entanglement, double slit interference and tunneling.

Examples will be the realization of Einsteins Gedankenexperiment on double slit interference where he proposed that measuring the momentum transfer to a double slit would unveil through which of the two slits the quantum particle had passed and new experiments on Helium dimers and trimers.

Das Gebiet der „Nanoplasmonik“ hat die einzigartigen lokalisierten Plasmon-Polaritonen in metallischen Nanopartikeln zum Thema. Die Forschung ist nicht neu: schon in der Bronze-Zeit wurden in Assyrien Kupfer-Nanopartikel - vermutlich wegen ihrer leuchtend rubinroten Farbe - hergestellt. Wesentliche Basis ist bis heute die elektrodynamische Theorie von Gustav Fedor Mie aus dem Jahre 1908. Experimentell wurden die Plasmon-Polaritonen erstmals 1970 identifiziert. Diese Theorie war die erste exakte Lösung der Maxwell’schen Gleichungen, allerdings unter schwerwiegenden Vereinfachungen, die oft, und speziell im Feld der metallischen Nanopartikel, nicht der experimentellen Realität entsprechen. Seit Faraday nahm die Zahl von Untersuchungen der PlasmonPolaritonen in metallischen Nanopartikeln in immenser Weise zu, aber mit ihnen wuchsen auch die Funde gravierender Differenzen zwischen Mie-Simulationsrechnungen und experimentellen Resultaten, die oft nicht auf Qualitätsmängel der Experimente sondern auf Mie’s Theorie selbst zurückzuführen sind. Dies hat natürlich das Interesse und die Suche nach „neuer“ Physik stetig weiter wachsen lassen und mündete schließlich in das aktuelle Gebiet der „Nanoplasmonik". Die stärksten Abweichungen und neuartigen Verhaltensweisen findet man in dem Bereich sehr kleiner Nanostrukturen zwischen, etwa 2 nm und 20 nm, d.h. in dem Übergangsbereich vom Festkörperpartikel zum „molekularen Cluster“. Teilweise sind sie heute verstanden, andere Eigenschaften aber warten immer noch auf ihre Aufklärung und erfordern weitere Forschungsanstrengungen. In dem Vortrag werden Beispiele grundlegender Abweichungen der Mie Theorie von der Realität vorgestellt und diskutiert.

Over the past years, nano-structured photonic materials have witnessed tremendous progress that has been driven both by a combination of advances in micro- and nano-fabrication, sophisticated characterization, and the development of a detailed theoretical understanding. In this talk, an – necessarily biased – overview of some of these aspects will be presented. Specifically, the focus will be on the development of three-dimensional Photonic Crystals and the modified radiation dynamics of emitters that are embedded in them as well as the extension of the Photonic-Crystal concept to periodic structures that include the so-called metamaterials whose properties are largely determined by plasmonic effects.

A theoretical analysis will be made on the inverse bremsstrahlung heating rate in Ar and Xe clusters irradiated by femtosecond laser pulses. The present analysis is based on the eikonal approximation (EA). In sharp contrast to the first Born approximation (FBA), EA contains higher-order contributions. The eikonal amplitude also satisfies the optical theorem within its range of validity. The calculations are performed using the plasma-screened Rogers potential introduced by Moll et al. (J. Phys. B 43 , 13503 (2010)) as well as the Debye potential for a wide range of experimental parameters. A comparison will be made between the predictions of EA with the corresponding results obtained in the FBA and classical methods.

Waveform controlled light fields offer the possibility to manipulate ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is a key to the design of electronic devices operating at up to petahertz frequencies. We have studied directional control of the electron emission from spherical SiO₂ nanoparticles in few-cycle laser fields with welldefined waveform. Projections of the three-dimensional electron momentum distributions were obtained via single-shot velocity-map imaging, where phase-tagging allowed retrieving the laser waveform for each laser shot. The application of this technique allowed us to efficiently suppress background contributions in the data and to obtain very accurate information on the amplitude and phase of the waveformdependent electron emission. The experimental data that is obtained for 4 fs pulses centered at 720 nm at different intensities in the range (1–4)×10¹³ W/cm² is compared to quasi-classical meanfield Monte-Carlo simulations. The model calculations identify electron backscattering from the nanoparticle surface in highly dynamical localized fields as the main process responsible for the energetic electron emission from the nanoparticles. Results on larger SiO₂ nanospheres up to 400 nm diameter show a significant influence of laser propagation effects on the electron emission pattern.

Improving the spatial resolution in time resolved experiments is of utmost importance for many applications of ultrafast laser spectroscopy. The high sensitivity and lateral resolution of the time-resolved photoemission electron microscopy technique (TR-PEEM) is used to verify simultaneous spatial and temporal control of nanooptical fields in the vicinity of metallic nanostructures and clusters.

I will demonstrate that adaptive shaping of the amplitude, phase and polarization of ultrashort laser pulses allows to switch between two different excitation patterns within a time scale that can be controlled almost freely and is limited only by the spectral bandwidth of the used coherent light source. This confirms that the polarization-shaped incident laser pulse can indeed be an effective tool for nanoscale localization of ultrashort optical excitation. In addition, I will discuss the future potential of such coherent control experiment in magnetism such as all optical switching on a nanoscale.

The Linac Coherent Light Source (LCLS) is a new, world wide unique Xray free electron laser (FEL), which produces ultrashort pulses up to 2keV with unprecedented brightness. One of the most promintent applications of this powerful tool is imaging of unrevealed ultrafast atomic and molecular processes. We report on the first imaging experiment realized at the LCLS. It was performed on single rare gas clusters, which are a simple model system for interaction between X-ray laser and matter.

Mit den modernen Methoden der Ultrakurzzeitspektroskopie ist es möglich, Femtosekunden-Laserpulse mit „maßgeschneiderter“ Pulsform, Momentanfrequenz und Polarisationszustand zu erzeugen. Ultrakurze geformte Laserpulse werden einerseits zur Untersuchung der Grundlagen der Wechselwirkung intensiver Laserpulse mit Materie eingesetzt und andererseits zur Kontrolle ultraschneller Reaktionen in der physikalischen Chemie.

Am Beispiel der selektiven Besetzung „bekleideter“ Zustände wird der Redner zeigen wie es gelingt, mit geformten intensiven Laserpulsen ultraschnelle atomare und molekulare Dynamik zu manipulieren. Darüber hinaus werden eine neue Methode zur tomographischen Rekonstruktion dreidimensionaler Elektronenwellenpakete mit Hilfe der abbildenden Photoelektronenspektroskopie vorgestellt und experimentelle Ergebnisse an chiralen Molekülen präsentiert.

Die nichtlineare Wechselwirkung intensiver Laserpulse eröffnet zudem neue Anwendungen in der Lasermikroskopie und Materialbearbeitung. Im Bereich der Lasermaterialbearbeitung werden Methoden der Nanostrukturierung und Analytik mit „maßgeschneiderten“ ultrakurzen Laserpulsen demonstriert. Anhand experimenteller Ergebnisse wird gezeigt, wie die Selbstphasenmodulation als Kontrastmechanismus in der nichtlinearen Mikroskopie genutzt werden kann.

Auf den ersten Blick sind Atomkerne und Metallcluster (metallische Nanoteilchen) grundverschiedene physikalische Systeme. Aus der Sicht der Vielteilchenphysik haben sie jedoch Vieles gemeinsam: magische Zahlen, mit der Teilchenzahl schnell veränderliche Deformationen (Jahn-Teller-Effekt), hervorstechende Resonanzanregungen, Spaltung/Fragmentation bei zunehmendem Coulombdruck. Natürlich gibt es auch große Unterschiede. Atome bestehen nur aus Nukleonen (mit etwa gleicher Masse) wohingegen Cluster aus (Valenz-)Elektronen und den wesentlich schwereren Ionen zusammengesetzt sind. Das hat Konsequenzen für die Dynamik. Vor allem aber unterscheiden sich die physikalischen Dimensionen um Größenordnungen. Damit ist der experimentelle Zugang grundverschieden. Messungen von Kerneigenschaften sind aufwendig. Clusterdynamik liegt in Reichweite heutiger Laser und ist damit wesentlich besser manipulierbar. Für die Theorie fallen diese Unterschiede kaum ins Gewicht. Darum ist die Modellierung beider Systeme sehr ähnlich.

Im Vortrag werden zuerst die Gemeinsamkeiten herausgearbeitet. Es wird die Möglichkeiten einer detaillierten theoretischen Beschreibung durch zeitabhängige Dichtefunktionaltheorie diskutiert. Im letzten Teil kommen die Unterschiede mehr zu tragen. Hier werden Beispiele aktueller Experimente und deren theoretischer Beschreibung vorgestellt, für Atomkerne die Stabilität superschwerer Elemente, für Cluster die Anregung durch intensive Laserpulse und die nachfolgende Elektronenund Ionendynamik.

Prof. Reinhard ist ein ausgewiesener Experte auf dem Gebiet der zeitabhängigen Dichtefunktionaltheorie und deren Anwendung auf Probleme der VielteilchenQuantendynamik endlicher Systeme. Im Mittelpunkt des Vortrages stehen die Mechanismen der Elektronenemission aus Clustern bei linearer und nichtlinearer Anregung durch Femtosekunden-Laserpulse und deren Signaturen in Photoelektronenspektren.

Der Freie-Elektronen-Laser FLASH am DESY liefert gepulste Strahlung im weichen Röntgenbereich. Diese ultrakurzen Pulse - kombiniert mit sichtbaren Laserpulsen in einer Pump-Probe-Anordnung - eröffnen neue Möglichkeiten, den Ablauf schneller photochemischer Reaktionen zu verfolgen. Das Studium solcher Prozesse auf deren natürlichen Zeitskala stellt allerdings hohe Anforderungen an die zeitliche Diagnostik. Es werden neue Methoden zur Einzelschussmessung der Pulsdauer von FLASH-Pulsen mit Hilfe einer Terahertz-Streak-Kamera sowie zur Einzelschussmessung der zeitlichen Verzögerung zwischen Röntgen- und Laserpulsen vorgestellt. Diese bilden die Basis für Experimente zur strahlungsinduzierten molekularen Dissoziation unter Beleuchtung mit zwei Pulsen vergleichbarer Intensität, aber dramatisch unterschiedlicher Wellenlänge von 800 nm bzw. 13 nm. Das Beispiel des Iod-Moleküls offenbart eine komplexe Dynamik, bei der verschiedene elektronische und chemische Prozesse - Auger-Zerfall, Tunnelionisation, Fragmentation - auf einer Zeitskala von 100 fs zusammenwirken.