Inst. Optik und Atomare Physik

213 Items

Recent Submissions
Vibronic optical spectroscopy of cryogenic flavin ions: the O2+ and N1 tautomers of protonated lumiflavin

Müller, David ; Dopfer, Otto (2020-08-04)

Flavins are key compounds in many photochemical and photophysical processes used by nature, because their optical properties strongly depend on the (de-)protonation site and solvation. Herein, we present the vibronic optical spectrum of protonated lumiflavin (H+LF), the parent molecule of the flavin family, obtained by visible photodissociation (VISPD) spectroscopy in a cryogenic ion trap. By c...

Ultrafast spin dynamics of a ferrimagnet revealed by femtosecond soft X-ray and XUV radiation

Hennecke, Martin Heinrich (2020)

In this thesis, we will present time-resolved experimental investigations of ultrafast spin phenomena in ferrimagnetic metallic alloys of GdFeCo. Recent studies of such ferrimagnetic systems have revealed that a femtosecond optical excitation is not only able to demagnetize such a system on a subpicosecond timescale, but also to permanently reverse its magnetization without any other external s...

Recent progress in the performance of HAPG based laboratory EXAFS and XANES spectrometers

Schlesiger, Christopher ; Praetz, Sebastian ; Gnewkow, Richard ; Malzer, Wolfgang ; Kanngießer, Birgit (2020-07-15)

New developments in the description and modeling of Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystals have led to the possibility of designing optimized optical solutions for X-ray absorption fine structure (XAFS) spectroscopy. XAFS is a very versatile method that is usually divided into two sub methods: extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge str...

Spectroscopic identification of fragment ions of DNA/RNA building blocks: the case of pyrimidine

Chatterjee, Kuntal ; Dopfer, Otto (2020-07-07)

Pyrimidine (Pym, 1,3-diazine, 1,3-diazabenzene) is an important N-heterocyclic building block of nucleobases. Understanding the structures of its fragment and precursor ions provides insight into its prebiotic and abiotic synthetic route. The long-standing controversial debate about the structures of the primary fragment ions of the Pym+ cation (C4H4N2+, m/z 80) resulting from loss of HCN, C3H3...

Quantitative magnetic particle imaging

Paysen, Hendrik (2020)

Magnetic particle imaging (MPI) is a noninvasive medical imaging technique introduced in 2005. MPI utilizes the unique properties of magnetic nanoparticles (MNP), which are of high interest for biomedical applications. One major advantage compared to other imaging modalities is that MPI images contain quantitative information about the MNP distribution. This information is beneficial for many a...

Tuning trion binding energy and oscillator strength in a laterally finite 2D system: CdSe nanoplatelets as a model system for trion properties

Ayari, Sabrine ; Quick, Michael T. ; Owschimikow, Nina ; Christodoulou, Sotirios ; Bertrand, Guillaume H. V. ; Artemyev, Mikhail ; Moreels, Iwan ; Woggon, Ulrike ; Jaziri, Sihem ; Achtstein, Alexander W. (2020-06-22)

We present a theoretical study combined with experimental validations demonstrating that CdSe nanoplatelets are a model system to investigate the tunability of trions and excitons in laterally finite 2D semiconductors. Our results show that the trion binding energy can be tuned from 36 meV to 18 meV with the lateral size and decreasing aspect ratio, while the oscillator strength ratio of trions...

Microhydration of protonated biomolecular building blocks: protonated pyrimidine

Chatterjee, Kuntal ; Dopfer, Otto (2020-05-27)

Protonation and hydration of biomolecules govern their structure, conformation, and function. Herein, we explore the microhydration structure in mass-selected protonated pyrimidine–water clusters (H+Pym–Wn, n = 1–4) by a combination of infrared photodissociation spectroscopy (IRPD) between 2450 and 3900 cm−1 and density functional theory (DFT) calculations at the dispersion-corrected B3LYP-D3/a...

Nonlocal ultrafast demagnetization dynamics of Co/Pt multilayers by optical field enhancement

Korff Schmising, Clemens von ; Giovannella, M. ; Weder, David ; Schaffert, Stefan ; Webb, J. L. ; Eisebitt, Stefan (2015)

The influence on ultrafast demagnetization dynamics of metallic nano-structured gratings deposited on thin films of magnetic Co/Pt multilayers is investigated by the time-resolved optical Kerr effect. Depending on the polarization of the pump pulse, a pronounced enhancement of the demagnetization amplitude is found. Calculation of the inhomogeneous optical field distribution due to plasmon inte...

Mask-based dual-axes tomoholography using soft x-rays

Guehrs, Erik ; Fohler, Manuel ; Frömmel, Stefanie ; Günther, Christian M. ; Hessing, Piet ; Schneider, Michael ; Shemilt, Laura ; Eisebitt, Stefan (2015)

We explore tomographic mask-based Fourier transform x-ray holography with respect to the use of a thin slit as a reference wave source. This imaging technique exclusively uses the interference between the waves scattered by the object and the slit simplifying the experimental realization and ensuring high data quality. Furthermore, we introduce a second reference slit to rotate the sample aroun...

The UE49 SGM RICXS beamline at BESSY II

Pietzsch, Annette ; Eisebitt, Stefan (2016)

Beamline UE49 SGM is a dedicated high flux soft x ray beamline, spanning the energy range of 95 eV to 1400 eV. Its micrometer focus makes it ideally suitable for investigation of small or inhomogeneous samples both with spectroscopic methods and coherent scattering as well as imaging techniques with full polarization control.

Mechanical Design of the MID Split-and-Delay Line at the European XFEL

Friedrich, B. ; Noll, Tino ; Lu, Wei ; Roth, T. ; Madsen, Anders ; Eisebitt, Stefan (2016)

A new split-and-delay line (SDL) is under development for the Materials Imaging and Dynamics (MID) end station at the European XFEL.* The device utilises Bragg reflection to provide pairs of X-ray pulses with an energy of (5 - 10) keV and a continuously tunable time delay of (-10 - 800) ps - thus allowing zero-crossing of the time delay. The mechanical concept features separate positioning stag...

Multi-Color Imaging of Magnetic Co/Pt Multilayers

Weder, David ; Korff Schmising, Clemens von ; Willems, Felix ; Günther, Christian M. ; Schneider, Michael ; Pfau, Bastian ; Merhe, A. ; Jal, Emmanuelle ; Vodungbo, Boris ; Lüning, Jan ; Mahieu, B. ; Capotondi, F. ; Pedersoli, Emanuele ; Eisebitt, Stefan (2017)

We demonstrate for the first time the realization of a spatial resolved two color, element-specific imaging experiment at the free-electron laser facility FERMI. Coherent imaging using Fourier transform holography was used to achieve direct real space access to the nanometer length scale of magnetic domains of Co/Pt heterostructures via the element-specific magnetic dichroism in the extreme ult...

Achieving diffraction-limited resolution in soft-X-ray Fourier-transform holography

Geilhufe, Jan ; Pfau, Bastian ; Günther, Christian M. ; Schneider, Michael ; Eisebitt, Stefan (2020)

The spatial resolution of microscopic images acquired via X-ray Fourier-transform holography is limited by the source size of the reference wave and by the numerical aperture of the detector. We analyze the interplay between both influences and show how they are matched in practice. We further identify, how high spatial frequencies translate to imaging artifacts in holographic reconstructions w...

CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump–probe experiments at the FLASH free-electron laser

Erk, Benjamin ; Müller, Jan P. ; Bomme, Cédric ; Boll, Rebecca ; Brenner, Günter ; Chapman, Henry N. ; Correa, Jonathan ; Düsterer, Stefan ; Dziarzhytski, Siarhei ; Eisebitt, Stefan ; Graafsma, Heinz ; Grunewald, Sören ; Gumprecht, Lars ; Hartmann, Robert ; Hauser, Günter ; Keitel, Barbara ; Korff Schmising, Clemens von ; Kuhlmann, Marion ; Manschwetus, Bastian ; Mercadier, Laurent ; Müller, Erland ; Passow, Christopher ; Plönjes, Elke ; Ramm, Daniel ; Rompotis, Dimitrios ; Rudenko, Artem ; Rupp, Daniela ; Sauppe, Mario ; Siewert, Frank ; Schlosser, Dieter ; Strüder, Lothar ; Swiderski, Angad ; Techert, Simone ; Tiedtke, Kai ; Tilp, Thomas ; Treusch, Rolf ; Schlichting, Ilme ; Ullrich, Joachim ; Moshammer, Robert ; Möller, Thomas ; Rolles, Daniel (2018)

The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, a...

Experimental evaluation of signal-to-noise in spectro-holography via modified uniformly redundant arrays in the soft x-ray and extreme ultraviolet spectral regime

Günther, Christian M. ; Guehrs, Erik ; Schneider, Michael ; Pfau, Bastian ; Korff Schmising, Clemens von ; Geilhufe, Jan ; Schaffert, Stefan ; Eisebitt, Stefan (2017)

We present dichroic x-ray lensless magnetic imaging by Fourier transform holography with an extended reference scheme via a modified uniformly redundant array (mURA). Holographic images of magnetic domains simultaneously generated by a single pinhole reference as well as by a mURA reference are compared with respect to the signal-to-noise ratio (SNR) as a function of exposure time. We apply thi...

Terahertz magnetic field enhancement in an asymmetric spiral metamaterial

Polley, Debanjan ; Hagström, Nanna Zhou ; Korff Schmising, Clemens von ; Eisebitt, Stefan ; Bonetti, Stefano (2018)

We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We ...

Indirect excitation of ultrafast demagnetization

Vodungbo, Boris ; Tudu, Bharati ; Perron, Jonathan ; Delaunay, Renaud ; Müller, Leonard ; Berntsen, Magnus H. ; Grübel, Gerhard ; Malinowski, Grégory ; Weier, Christian ; Gautier, Julien ; Lambert, Guillaume ; Zeitoun, Philippe ; Gutt, Christian ; Jal, Emmanuelle ; Reid, Alexander H. ; Granitzka, Patrick W. ; Jaouen, Nicolas ; Dakovski, Georgi L. ; Moeller, Stefan ; Minitti, Michael P. ; Mitra, Ankush ; Carron, Sebastian ; Pfau, Bastian ; Korff Schmising, Clemens von ; Schneider, Michael ; Eisebitt, Stefan ; Lüning, Jan (2016)

Does the excitation of ultrafast magnetization require direct interaction between the photons of the optical pump pulse and the magnetic layer? Here, we demonstrate unambiguously that this is not the case. For this we have studied the magnetization dynamics of a ferromagnetic cobalt/palladium multilayer capped by an IR-opaque aluminum layer. Upon excitation with an intense femtosecond-short IR ...

Optical inter-site spin transfer probed by energy and spin-resolved transient absorption spectroscopy

Willems, Felix ; Korff Schmising, Clemens von ; Strüber, Christian ; Schick, Daniel ; Engel, Dieter W. ; Dewhurst, J. K. ; Elliott, Peter ; Sharma, Sangeeta ; Eisebitt, Stefan (2020)

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate ...

In situ single-shot diffractive fluence mapping for X-ray free-electron laser pulses

Schneider, Michael ; Günther, Christian M. ; Pfau, Bastian ; Capotondi, Flavio ; Manfredda, Michele ; Zangrando, Marco ; Mahne, Nicola ; Raimondi, Lorenzo ; Pedersoli, Emanuele ; Naumenko, Denys ; Eisebitt, Stefan (2018)

Free-electron lasers (FELs) in the extreme ultraviolet (XUV) and X-ray regime opened up the possibility for experiments at high power densities, in particular allowing for fluence-dependent absorption and scattering experiments to reveal non-linear light–matter interactions at ever shorter wavelengths. Findings of such non-linear effects are met with tremendous interest, but prove difficult to ...

Generating circularly polarized radiation in the extreme ultraviolet spectral range at the free-electron laser FLASH

Korff Schmising, Clemens von ; Weder, David ; Noll, Tino ; Pfau, Bastian ; Hennecke, Martin ; Strüber, Christian ; Radu, Ilie ; Schneider, Michael ; Staeck, Steffen ; Günther, Christian M. ; Lüning, Jan ; Merhe, Alaa el Dine ; Buck, Jens ; Hartmann, Gregor ; Viefhaus, Jens ; Treusch, Rolf ; Eisebitt, Stefan (2017)

A new device for polarization control at the free electron laser facility FLASH1 at DESY has been commissioned for user operation. The polarizer is based on phase retardation upon reflection off metallic mirrors. Its performance is characterized in three independent measurements and confirms the theoretical predictions of efficient and broadband generation of circularly polarized radiation in t...