Investigation of the hydrated 7-hydroxy-4-methylcoumarin dimer by combined IR/UV spectroscopy.

The first molecular beam investigations on a coumarin dimer and clusters of a coumarin dimer with water both in the neutral (S0) and cationic (D0) electronic ground state are performed. The structure and structural changes due to ionization of the isolated 7-hydroxy-4-methylcoumarin dimer (7H4MC)2 as well as its mono- and dihydrate (7H4MC)2(H2O)1-2 are analyzed by applying combined IR/UV spectroscopy compared with density functional theory calculations. In case of the neutral dimer of 7H4MC a doubly hydrogen-bonded structure is formed.

Topological growing of Laughlin states in synthetic gauge fields.

We suggest a scheme for the preparation of highly correlated Laughlin states in the presence of synthetic gauge fields, realizing an analogue of the fractional quantum Hall effect in photonic or atomic systems of interacting bosons. It is based on the idea of growing such states by adding weakly interacting composite fermions along with magnetic flux quanta one by one. The topologically protected Thouless pump ("Laughlin's argument") is used to create two localized flux quanta and the resulting hole excitation is subsequently filled by a single boson, which, together with one of the flux quanta, forms a composite fermion.

Note: Reliable low-vibration piezo-mechanical shutter.

We present a mechanical shutter based on a bending piezo-actuator. The shutter features an active aperture of about 2 mm, allowing for full extinction and lossless transmission of a beam. Acoustic noise and mechanical vibrations produced are very low and the shutter is outstandingly long-lived; a test device has undergone 20 × 10(6) cycles without breaking.

A combined IR/IR and IR/UV spectroscopy study on the proton transfer coordinate of isolated 3-hydroxychromone in the electronic ground and excited state.

In this paper the excited state proton transfer (ESPT) of isolated 3-hydroxychromone (3-HC), the prototype of the flavonols, is investigated for the first time by combined IR/UV spectroscopy in molecular beam experiments. The IR/UV investigations are performed both for the electronically excited and electronic ground state indicating a spectral overlap of transitions of the 3-HC monomer and clusters with water in the electronic ground state, whereas in the excited state only the IR frequencies of the proton-transferred monomer structure are observed. Due to the loss of isomer and species selectivity with respect to the UV excitations IR/IR techniques are applied in order to figure out the assignment of the vibrational transitions in the S0 state.

All-optical control of ferromagnetic thin films and nanostructures.

The interplay of light and magnetism allowed light to be used as a probe of magnetic materials. Now the focus has shifted to use polarized light to alter or manipulate magnetism. Here, we demonstrate optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording.

In-depth exploration of the photophysics of a trinuclear palladium complex.

A detailed theoretical and spectroscopic study on the electronically excited states of a trinuclear palladium complex is presented both in the gas phase and solution. The application of DFT and TDDFT methods as well as a variety of spectroscopic methods to the chosen complex [Pd3{Si(mt(Me))3}2] (1, mt(Me) = methimazole) leads to the first detailed analysis of the photophysics of a symmetric trinuclear complex. In combination with the calculations, energies, structures and lifetimes of the excited electronic states (with an (3)A1 state as the lowest one) are characterized by applying the resonant-2-photon-ionization method in a molecular beam experiment as well as luminescence, time-correlated single photon counting and excited state femtosecond absorption spectroscopy in solution.

Engineered materials for all-optical helicity-dependent magnetic switching.

The possibility of manipulating magnetic systems without applied magnetic fields have attracted growing attention over the past fifteen years. The low-power manipulation of the magnetization, preferably at ultrashort timescales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization in engineered magnetic materials.

Novel materials for biofilm reactors and their characterization.

The application of adherently growing microorganisms for biotechnological production processes is established, but it is still a niche technology with only a small economic impact. However, novel approaches are under development for new types of biofilm reactors. In this context, increasingly more microstructured metal surfaces are being investigated, and they show positive effects on the bacterial growth and the biofilm establishment.

Feedback effect during ultrafast demagnetization dynamics in ferromagnets.

Motivated by the recent controversy about the importance of spin-flip scattering for ultrafast demagnetization in ferromagnets, we study the spin-dependent electron dynamics based on a dynamical Elliott-Yafet mechanism. The key improvement to earlier approaches is the use of a modified Stoner model with a dynamic exchange splitting between majority and minority bands. In the framework of our microscopic model, we find a novel feedback effect between the time-dependent exchange splitting and the spin-flip scattering.

Chiral edge states and fractional charge separation in a system of interacting bosons on a kagome lattice.

We consider the extended hard-core Bose-Hubbard model on a kagome lattice with boundary conditions on two edges. We find that the sharp edges lift the degeneracy and freeze the system into a striped order at 1/3 and 2/3 filling for zero hopping. At small hopping strengths, holes spontaneously appear and separate into fractional charges which move to the edges of the system.

ESIPT and photodissociation of 3-hydroxychromone in solution: photoinduced processes studied by static and time-resolved UV/Vis, fluorescence, and IR spectroscopy.

The spectral properties of fluorescence sensors such as 3-hydroxychromone (3-HC) and its derivatives are sensitive to interaction with the surrounding medium as well as to substitution. 3-HC is a prototype system for other derivatives because it is the basic unit of all flavonoides undergoing ESIPT and is not perturbed by a substituent. In this study, the elementary processes and intermediate states in the photocycle of 3-HC as well as its anion were identified and characterized by the use of static and femtosecond time-resolved spectroscopy in different solvents (methylcyclohexane, acetonitrile, ethanol, and water at different pH).

In-plane focusing of terahertz surface waves on a gradient index metamaterial film.

We designed and implemented a gradient index metasurface for in-plane focusing of confined terahertz (THz) surface waves. We measured the spatial propagation of the surface waves by two-dimensional mapping of the complex electric field using a THz near-field spectroscope. The surface waves were focused to a diameter of 500 μm after a focal length of approximately 2 mm.

Topological edge States in the one-dimensional superlattice Bose-Hubbard model.

We analyze interacting ultracold bosonic atoms in a one-dimensional superlattice potential with alternating tunneling rates t1 and t2 and inversion symmetry, which is the bosonic analogue of the Su-Schrieffer-Heeger model. A Z2 topological order parameter is introduced which is quantized for the Mott insulating (MI) phases. Depending on the ratio t1/t2 the n=1/2 MI phase is topologically nontrivial, which results in many-body edge states at open boundaries.

Enhancing protein adsorption simulations by using accelerated molecular dynamics.

The atomistic modeling of protein adsorption on surfaces is hampered by the different time scales of the simulation ([Formula: see text][Formula: see text]s) and experiment (up to hours), and the accordingly different 'final' adsorption conformations. We provide evidence that the method of accelerated molecular dynamics is an efficient tool to obtain equilibrated adsorption states. As a model system we study the adsorption of the protein BMP-2 on graphite in an explicit salt water environment.

Peptide dissociation patterns in secondary ion mass spectrometry under large argon cluster ion bombardment.

Rationale: The analysis of organic and biological substances by secondary ion mass spectrometry (SIMS) has greatly benefited from the use of cluster ions as primary bombarding species. Thereby, depth profiling and three-dimensional (3D) imaging of such systems became feasible. Large Ar(n)(+) cluster ions may constitute a further improvement in this direction.

Closed and open system dynamics in a fermionic chain with a microscopically specified bath: relaxation and thermalization.

We study thermalization in a one-dimensional quantum system consisting of a noninteracting fermionic chain with each site of the chain coupled to an additional bath site. Using a density matrix renormalization group algorithm we investigate the time evolution of the observables in the chain after a quantum quench. For low densities we show that the intermediate time dynamics can be quantitatively described by a system of coupled equations of motion.

Rydberg polaritons in a cavity: a superradiant solid.

We study an optical cavity coupled to a lattice of Rydberg atoms, which can be represented by a generalized Dicke model. We show that the competition between the atom-atom interaction and atom-light coupling induces a rich phase diagram. A novel superradiant solid (SRS) phase is found, where both the superradiance and crystalline orders coexist.

Controlling the dynamics of an open many-body quantum system with localized dissipation.

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement.

Active aberration- and point-spread-function control in direct laser writing.

We control the point-spread-function of high numerical aperture objectives used for direct laser writing with a spatial light modulator. Combining aberration correction with different types of amplitude filters to reduce the aspect ratio of the point-spread-function enhances the structural and optical quality of woodpile photonic crystals. Here, aberration correction is crucial to ensure the functionality of the filters.

Bottom-up assembly of photonic crystals.

In this tutorial review we highlight fundamental aspects of the physics underpinning the science of photonic crystals, provide insight into building-block assembly routes to the fabrication of different photonic crystal structures and compositions, discuss their properties and describe how these relate to function, and finally take a glimpse into future applications.

Desolvation of macromolecules by ultrafast heating: A molecular-dynamics study.

Using molecular-dynamics simulation, we investigate the consequences of ultrafast laser-induced heating of a water droplet containing a solvated polymer, using the example of a 1 ps laser irradiation. We study the isolation process and the properties of the isolated polymer as a function of the polymer size, the droplet size, and the temperature to which the droplet is heated. We find that the isolation process occurs on a time scale of a few ten ps.

Spectrally wide-band terahertz wave modulator based on optically tuned graphene.

New applications in the realms of terahertz (THz) technology require versatile adaptive optics and powerful modulation techniques. Semiconductors have proven to provide fast all-optical terahertz wave modulation over a wide frequency band. We show that the attenuation and modulation depth in optically driven silicon modulators can be significantly enhanced by deposition of graphene on silicon (GOS).

IR and IR + UV spectroscopy of isolated [Al-AcPheOMe]n+ cluster cations (n = 1, 3).

Singly and triply charged cationic clusters of aluminium and the protected amino acid AcPheOMe are investigated in a supersonic beam by using a combination of a thermic and a laser ablation ion source. For the singly charged species UV- and IR photodissociation spectroscopy is applied. In the case of the triply charged clusters a variant of combined IR + UV spectroscopy is used to obtain information in the NH-stretching region.