Optimierung der EUV-Emission aus Argon-Mikrotropfen durch geformte intensive Femtosekunden-Laserpulse

In der Wechselwirkung intensiver, ultrakurzer Laserpulse mit Mikrometer-großen Tropfen werden die Tropfen ionisiert, und es bildet sich ein Plasma. In dieser Arbeit wird die Laser-Tropfen-Wechselwirkung anhand der Plasmaemission im extrem-ultravioletten (EUV) Wellenlängenbereich untersucht. Die Spektroskopie der Emission ermöglicht die Charakterisierung des Plasmazustandes und liefert Rückschlüsse über den Ablauf der Wechselwirkung. Durch die gezielte Formung der Laserpulse in Amplitude und Phase wird die Anregung an die Dynamik des Plasmas angepasst und die EUV-Emission deutlich erhöht.In the interaction of intense ultra-short laser pulses with micrometer sized droplets, the droplets are ionised and transformed into a plasma. In this work, the laser-droplet-interaction is studied based on the plasma emission in the extreme ultraviolet (EUV) spectral range. The spectroscopy of the emission allows for analysing the plasma state and the interaction sequence. Applying shaped laser pulses, the excitation is adapted to the plasma dynamics resulting in an enhanced EUV yield

Melting, bubble-like expansion and explosion of superheated plasmonic nanoparticles

We report on time-resolved coherent diffraction imaging of gas-phase silver nanoparticles, strongly heated via their plasmon resonance. The x-ray diffraction images reveal a broad range of phenomena for different excitation strengths, from simple melting over strong cavitation to explosive disintegration. Molecular dynamics simulations fully reproduce this behavior and show that the heating induces rather similar trajectories through the phase diagram in all cases, with the very different outcomes being due only to whether and where the stability limit of the metastable superheated liquid is crossed.Comment: 17 pages, 8 figures (including supplemental material

Publisher Correction: Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters

The original PDF version of this Article contained an error in Equation 1. The original HTML version of this Article contained errors in Equation 2 and Equation 4. These errors have now been corrected in both the PDF and the HTML versions of the Article

Publisher Correction: Nanoplasmonic electron acceleration by attosecond-controlled forward rescattering in silver clusters (Nature communications (2017) 8 1 (1181))

The original PDF version of this Article contained an error in Equation 1. The original HTML version of this Article contained errors in Equation 2 and Equation 4. These errors have now been corrected in both the PDF and the HTML versions of the Article. The original PDF version of this Article contained an error in Equation 1. A dot over the first occurrence of the variable ri was missing, and incorrectly read: (Formula Presented). The correct form of Equation 1 is as follows: (Formula Presented). This has now been corrected in the PDF version of the Article. The HTML version was correct from the time of publication. The original HTML version of this Article contained errors in Equation 2 and Equation 4. In Equation 2, a circle over the first occurrence of the variable ri replaced the intended dot, and incorrectly read: (Formula Presented). The correct form of Equation 2 is as follows: (Formula Presented). In Equation 4, circles over the first and fifth occurrences of the variable ri replaced the intended dots, and incorrectly read: (Formula Presented). The correct form of Equation 4 is as follows: (Formula Presented). This has now been corrected in the HTML version of the Article. The PDF version was correct from the time of publication

Mapping long-lived dark states in copper porphyrin nanostructures

Long-lived excited states in molecular aggregates are a promising route for efficient energy transfer with potential applications in optoelectronic devices. Spatially resolved optical detection of these states is challenging due to a critical trade-off between sufficiently high photon emission rates and negligible contribution of the luminescence channel to the total lifetime. Here, we report on selective mapping of excited states in copper tetraundecylporphyrin (CuTUP) assemblies on graphite (HOPG) using two-photon photoemission electron microscopy. While the photoemission electron microscopy (PEEM) data are consistent with time-resolved luminescence measurements on a nanosecond time scale, additional long-lived states with lifetimes in the microsecond range are found with nondetectable emission of photons. These,dark states serve as initial states in a subsequent photoemission process, giving rise to a high yield and, pronounced lateral contrast. In combination with long-range corrected density functional theory (DFT) we analyze the energetics and nature of contributing states. Our study underlines the versatility and specificity of excitation nanoscopy by PEEM enabling high spatial resolution beyond the wavelength limit

Three-dimensional femtosecond snapshots of isolated faceted nanostructures

The structure and dynamics of isolated nanosamples in free flight can be directly visualized via single-shot coherent diffractive imaging using the intense and short pulses of x-ray free-electron lasers. Wide-angle scattering images encode three-dimensional (3D) morphological information of the samples, but its retrieval remains a challenge. Up to now, effective 3D morphology reconstructions from single shots were only achieved via fitting with highly constrained models, requiring a priori knowledge about possible geometries. Here, we present a much more generic imaging approach. Relying on a model that allows for any sample morphology described by a convex polyhedron, we reconstruct wide-angle diffraction patterns from individual silver nanoparticles. In addition to known structural motives with high symmetries, we retrieve imperfect shapes and agglomerates that were not previously accessible. Our results open unexplored routes toward true 3D structure determination of single nanoparticles and, ultimately, 3D movies of ultrafast nanoscale dynamics.ISSN:2375-254

Probing near-solid density plasmas using soft x-ray scattering

X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm-3 and an electron temperature of 14 ± 3.5 eV. In pump-probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data. © 2010 IOP Publishing Ltd

Three-dimensional femtosecond snapshots of isolated faceted nanostructures

The structure and dynamics of isolated nanosamples in free flight can be directly visualized via single-shot coherent diffractive imaging using the intense and short pulses of x-ray free-electron lasers. Wide-angle scattering images encode three-dimensional (3D) morphological information of the samples, but its retrieval remains a challenge. Up to now, effective 3D morphology reconstructions from single shots were only achieved via fitting with highly constrained models, requiring a priori knowledge about possible geometries. Here, we present a much more generic imaging approach. Relying on a model that allows for any sample morphology described by a convex polyhedron, we reconstruct wide-angle diffraction patterns from individual silver nanoparticles. In addition to known structural motives with high symmetries, we retrieve imperfect shapes and agglomerates that were not previously accessible. Our results open unexplored routes toward true 3D structure determination of single nanoparticles and, ultimately, 3D movies of ultrafast nanoscale dynamics