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- ItemPreparation of clay mineral samples for high resolution x-ray imaging(Bristol : Institute of Physics Publishing, 2013) Abbati, G.; Seim, C.; Legall, H.; Stiel, H.; Thomas, N.; Wilhein, T.In the development of optimum ceramic materials for plastic forming, it is of fundamental importance to gain insight into the compositions of the clay minerals. Whereas spectroscopic methods are adequate for determining the elemental composition of a given sample, a knowledge of the spatial composition, together with the shape and size of the particles leads to further, valuable insight. This requires an imaging technique such as high resolution X-ray microscopy. In addition, fluorescence spectroscopy provides a viable element mapping technique. Since the fine particle fraction of the materials has a major effect on physical properties like plasticity, the analysis is focused mainly on the smallest particles. To separate these from the bigger agglomerates, the raw material has to pass through several procedures like centrifugation and filtering. After that, one has to deposit a layer of appropriate thickness on to a suitable substrate. These preparative techniques are described here, starting from the clay mineral raw materials and proceeding through to samples that are ready to analyze. First results using high resolution x-ray imaging are shown.
- ItemAtomic processes in bicircular fields(Bristol : IOP Publ., 2016) Odžak, S.; Hasović, E.; Becker, W.; Milošević, D.B.We investigate laser-assisted electron-ion recombination (LAR), high-order harmonic generation (HHG) and above-threshold ionization (ATI) of argon atoms by a bicircular laser field, which consists of two coplanar counter-rotating circularly polarized fields of frequencies rω and sω. The energy of soft x rays generated in the LAR process is analyzed as a function of the incident electron angle and numerical results of direct recombination of electrons with Ar+ ions are presented. We also present the results of HHG by a bicircular field and confirm the selection rules derived earlier for inert-gas atoms in a p ground state. We show that the photoelectron spectra in the ATI process, presented in the momentum plane, as well as the LAR spectra exhibit the same discrete rotational symmetry as the applied field.
- ItemAttosecond time delays in C60 valence photoemissions at the giant plasmon(Bristol : IOP Publ., 2015) Barillot, T.; Magrakvelidze, M.; Loriot, V.; Bordas, C.; Hervieux, P.-A.; Gisselbrecht, M.; Johnsson, P.; Laksman, J.; Mansson, E.P.; Sorensen, S.; Canton, S.E.; Dahlström, J.M.; Dixit, G.; Madjet, M.E.; Lépine, F.; Chakraborty, H.S.We perform time-dependent local density functional calculations of the time delay in C60 HOMO and HOMO-1 photoionization at giant plasmon energies. A semiclassical model is used to develop further insights.
- ItemPhotoelectron holography in strong optical and dc electric fields(Bristol : Institute of Physics Publishing, 2014) Stodolna, A.; Huismans, Y.; Rouzée, A.; Lépine, F.; Vrakking, M.J.J.The application of velocity map imaging for the detection of photoelectrons resulting from atomic or molecular ionization allows the observation of interferometric, and in some cases holographic structures that contain detailed information on the target from which the photoelecrons are extracted. In this contribution we present three recent examples of the use of photoelectron velocity map imaging in experiments where atoms are exposed to strong optical and dc electric fields. We discuss (i) observations of the nodal structure of Stark states of hydrogen measured in a dc electric field, (ii) mid-infrared strong-field ionization of metastable Xe atoms and (iii) the reconstruction of helium electronic wavepackets in an attosecond pump-probe experiment. In each case, the interference between direct and indirect electron pathways, reminiscent of the reference and signal waves in holography, is seen to play an important role.
- ItemCorrelated electronic decay following intense near-infrared ionization of clusters(Bristol : IOP Publ., 2015) Schütte, Bernd; Arbeiter, Mathias; Fennel, Thomas; Jabbari, Ghazal; Kuleff, Alexander I.; Vrakking, Marc J. J.; Rouzée, ArnaudWe report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.
- ItemControllable Laser Ion Acceleration(Bristol : IOP Publ., 2016) Kawata, S.; Kamiyama, D.; Ohtake, Y.; Takano, M.; Barada, D.; Kong, Q.; Wang, P.X.; Gu, Y.J.; Wang, W.M.; Limpouch, J.; Andreev, A.; Bulanov, S.V.; Sheng, Z.M.; Klimo, O.; Psikal, J.; Ma, Y.Y.; Li, X.F.; Yu, Q.S.In this paper a future laser ion accelerator is discussed to make the laser-based ion accelerator compact and controllable. Especially a collimation device is focused in this paper. The future laser ion accelerator should have an ion source, ion collimators, ion beam bunchers, and ion post acceleration devices [Laser Therapy 22, 103(2013)]: the ion particle energy and the ion energy spectrum are controlled to meet requirements for a future compact laser ion accelerator for ion cancer therapy or for other purposes. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching would be successfully realized by a multistage laser-target interaction.
- ItemA compact laboratory transmission X-ray microscope for the water window(Bristol : Institute of Physics Publishing, 2013) Legall, H.; Stiel, H.; Blobel, G.; Seim, C.; Baumann, J.; Yulin, S.; Esser, D.; Hoefer, M.; Wiesemann, U.; Wirtz, M.; Schneider, G.; Rehbein, S.; Hertz, H.M.In the water window (2.2-4.4 nm) the attenuation of radiation in water is significantly smaller than in organic material. Therefore, intact biological specimen (e.g. cells) can be investigated in their natural environment. In order to make this technique accessible to users in a laboratory environment a Full-Field Laboratory Transmission X-ray Microscope (L-TXM) has been developed. The L-TXM is operated with a nitrogen laser plasma source employing an InnoSlab high power laser system for plasma generation. For microscopy the Ly α emission of highly ionized nitrogen at 2.48 nm is used. A laser plasma brightness of 5 × 1011 photons/(s × sr × μm2 in line at 2.48 nm) at a laser power of 70 W is demonstrated. In combination with a state-of-the-art Cr/V multilayer condenser mirror the sample is illuminated with 106 photons/(μm2 × s). Using objective zone plates 35-40 nm lines can be resolved with exposure times < 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W. These exposure times enable cryo tomography in a laboratory environment.
- ItemCharacterization of self-modulated electron bunches in an argon plasma(Bristol : IOP Publ., 2018) Gross, M.; Lishilin, O.; Loisch, G.; Boonpornprasert, P.; Chen, Y.; Engel, J.; Good, J.; Huck, H.; Isaev, I.; Krasilnikov, M.; Li, X.; Niemczyk, R.; Oppelt, A.; Qian, H.; Renier, Y.; Stephan, F.; Zhao, Q.; Brinkmann, R.; Martinez de la Ossa, A.; Osterhoff, J.; Grüner, F.J.; Mehrling, T.; Schroeder, C.B.; Will, I.The self-modulation instability is fundamental for the plasma wakefield acceleration experiment of the AWAKE (Advanced Wakefield Experiment) collaboration at CERN where this effect is used to generate proton bunches for the resonant excitation of high acceleration fields. Utilizing the availability of flexible electron beam shaping together with excellent diagnostics including an RF deflector, a supporting experiment was set up at the electron accelerator PITZ (Photo Injector Test facility at DESY, Zeuthen site), given that the underlying physics is the same. After demonstrating the effect [1] the next goal is to investigate in detail the self-modulation of long (with respect to the plasma wavelength) electron beams. In this contribution we describe parameter studies on self-modulation of a long electron bunch in an argon plasma. The plasma was generated with a discharge cell with densities in the 1013 cm-3 to 1015 cm-3 range. The plasma density was deduced from the plasma wavelength as indicated by the self-modulation period. Parameter scans were conducted with variable plasma density and electron bunch focusing.
- ItemMolecular above-threshold ionization spectra as an evidence of the three-point interference of electron wave packets(Bristol : IOP Publ., 2015) Hasović, Elvedin; Milošević, Dejan B.; Gazibegović-Busuladži, Azra; Čerkić, Aner; Busuladžić, MustafaWe consider high-order above-threshold ionization (HATI) of polyatomic molecules ionized by a strong linearly polarized laser field. Improved molecular strong-field approximation by which the HATI process on polyatomic molecular species can be described is developed. Using this theory we calculate photoelectron angular-energy spectra for different triatomic molecules. Special attention is devoted to the minima that are observed in the calculated high-energy electron spectra of the ozone and carbon dioxide molecules. A key difference between these minima and minima that are observed in the corresponding spectra of diatomic molecules are presented.
- ItemSetup of an 8 keV laboratory transmission x-ray microscope(Bristol : Institute of Physics Publishing, 2014) Baumbach, S.; Kanngießer, B.; Malzer, W.; Stiel, H.; Bjeoumikhova, S.; Wilhein, T.This article presents a concept and the first results for the setup of an 8keV laboratory transmission x-ray microscope with a polycapillary optic as condenser at the BliX in Berlin. The incentive of building such a microscope is that the penetration depth for hard x-rays is much higher than in the soft x-ray range, e.g. The water window. Therefore, it is possible to investigate even dense materials such as metal compounds, bones or geological samples. The future aim is to achieve a spatial resolution better than 200 nm.