Soft X-ray imaging with coherence tomography in the water window spectral range using high-harmonic generation
Autoren
J. Reinhard, F. Wiesner, M. Hennecke, T. Sidiropoulos, S. Kaleta, J. Späthe, J. Abel, M. Wünsche, G. Schmidl, J. Plentz, U. Hübner, K. Freiberg, J. Apell, S. Lippmann, M. Schnürer, S. Eisebitt, G. Paulus, S. Fuchs
Erscheinungsjahr
Erschienen in:
Light: Science and Applications
High-harmonic generation (HHG) is used as a source for various imaging applications in the extreme ultraviolet spectral range. It offers spatially coherent radiation and unique elemental contrast with the potential for attosecond time resolution. The unfavorable efficiency scaling to higher photon energies prevented the imaging application in the soft X-ray range so far. In this work we demonstrate the feasibility of using harmonics for imaging in the water window spectral region (284 eV to 532 eV). We achieve nondestructive depth profile imaging in a heterostructure by utilizing a broadband and noise-resistant technique called soft X-ray Coherence Tomography (SXCT) at a high-flux lab-scale HHG source. SXCT is derived from Optical Coherence Tomography, a Fourier based technique that can use the full bandwidth of the source to reach an axial resolution of 12 nm in this demonstration. The employed source covers the entire water window, with a photon flux exceeding 10 ⁶ photons/eV/s at a photon energy of 500 eV. We show local cross sections of a sample consisting of Aluminium oxide and Platinum layers of varying thickness on a Zinc oxide substrate. We validate the findings with scanning and transmission electron microscopy after preparation with focused ion beam milling.
Coincidence measurement of two-photon double ionization of argon through an autoionizing resonance
Autoren
S. Hell, J. Späthe, M. Førre, R. Klas, J. Rothhardt, J. Limpert, R. Moshammer, C. Ott, G. Paulus, S. Fritzsche, M. Kübel
Erscheinungsjahr
Erschienen in:
Physical Review Research
We present coincidence measurements of two-photon double ionization (TPDI) of argon driven by femtosecond pulses tunable around 26.5eV photon energy, which are obtained from a high-harmonic generation source. The measured photoelectron spectra are interpreted with regard to three TPDI mechanisms. Theoretical predictions are obtained by an approximate model for direct TPDI and atomic structure calculations, which are implemented into a Monte Carlo simulation. The prevailing mechanism involves the excitation and prompt photoionization of an autoionizing resonance in neutral argon. We provide evidence for pronounced electron-electron interaction in this ultrafast ionization process. Furthermore, we show that the dominant TPDI mechanism can be altered by slight tuning of the photon energy. The present work paves the way for scrutinizing and controlling nonlinear photoionization in the extreme ultraviolet using table-top sources.
Optical Coherence Tomography of Van Der Waals Heterostructures Using Extreme Ultraviolet Light
Autoren
F. Wiesner, J. Abel, M. Hussain, V. Krishna, A. Cadore, J. Felipe, A. Valencia, M. Wünsche, J. Reinhard, M. Gruenewald, C. Cocchi, G. Paulus, G. Soavi, S. Fuchs
Erscheinungsjahr
Erschienen in:
Advanced Materials Interfaces
New experimental methods with high out-of-plane spatial sensitivity combined with ultrafast temporal resolution can revolutionize the understanding of charge- and heat-transfer dynamics occurring at interfaces. In this work, a step forward is taken in this direction by applying coherence tomography with extreme ultraviolet (EUV) light to different van der Waals heterostructures, which enables a 3D sample reconstruction with nanoscopic axial resolution. Furthermore, the measurements and, more in general, the approach is confirmed by ab initio calculations of the refractive index of layered materials that we compare to existing databases of empirical data. The EUV coherence tomography contrast is estimated in a broad spectral range (photon energy 65 –100 eV). This work sets the basis for the development of a new spectroscopy tool that, thanks to the temporal profile of EUV light sources and the high axial resolution of coherence tomography, can become the ideal probe of ultrafast processes occurring in van der Waals heterostructures and buried nanoscale opto-electronic devices.
Proof-of-principle experiment for the dark-field detection concept for measuring vacuum birefringence
Autoren
M. Šmíd, P. Khademi, N. Ahmadiniaz, M. Andrzejewski, C. Baehtz, E. Brambrink, J. Bulička, T. Burian, S. Cafiso, J. Chalupský, T. Cowan, S. Göde, J. Grenzer, V. Hájková, P. Hilz, W. Hippler, H. Höppner, A. Horynová, L. Huang, O. Humphries, Š. Jelínek, L. Juha, F. Karbstein, C. Kohlfürst, A. Garcia, R. Lötzsch, M. Masruri, A. Matheron, M. Nakatsutsumi, G. Paulus, A. Pelka, T. Preston, S. Rahul, L. Randolph, A. Sävert, H. Schlenvoigt, R. Schützhold, J. Schwinkendorf, T. Stöhlker, M. Toncian, T. Toncian, M. Valialshchikov, V. Vozda, E. Weckert, C. Wessel, J. Wild, U. Zastrau, M. Zepf
Erscheinungsjahr
Erschienen in:
Physical Review A
Vacuum fluctuations give rise to effective nonlinear interactions between electromagnetic fields. These generically modify the characteristics of light traversing a strong-field region. X-ray free-electron lasers (XFELs) constitute a particularly promising probe, due to their brilliance, the possibility of precise control and favorable frequency scaling. However, the nonlinear vacuum response is very small even when probing a tightly focused high-intensity laser field with XFEL radiation and direct measurement of light-by-light scattering of real photons and the associated fundamental physics constants of the quantum vacuum has not been possible to date. Achieving a sufficiently good signal-to-background separation is key to a successful quantum vacuum experiment. To master this challenge, a dark-field detection concept has recently been proposed. Here we present the results of a proof-of-principle experiment validating this approach by demonstrating that using real-world x-ray optics the background signal can be suppressed sufficiently to measure the weak nonlinear response of the vacuum.
Towards a vacuum birefringence experiment at the Helmholtz International Beamline for Extreme Fields (Letter of Intent of the BIREF@HIBEF Collaboration)
Autoren
N. Ahmadiniaz, C. Bähtz, A. Benediktovitch, C. Bömer, L. Bocklage, T. Cowan, J. Edwards, S. Evans, S. Franchino Viñas, H. Gies, S. Göde, J. Görs, J. Grenzer, U. Hernandez Acosta, T. Heinzl, P. Hilz, W. Hippler, L. Huang, O. Humphries, F. Karbstein, P. Khademi, B. King, T. Kluge, C. Kohlfürst, D. Krebs, A. Laso-García, R. Lötzsch, A. Macleod, B. Marx-Glowna, E. Mosman, M. Nakatsutsumi, G. Paulus, S. Rahul, L. Randolph, R. Röhlsberger, N. Rohringer, A. Sävert, S. Sadashivaiah, R. Sauerbrey, H. Schlenviogt, S. Schmidt, U. Schramm, R. Schützhold, J. Schwinkendorf, D. Seipt, M. Šmíd, T. Stöhlker, T. Toncian, M. Valialshchikov, A. Wipf, U. Zastrau, M. Zepf
Erscheinungsjahr
Erschienen in:
High Power Laser Science and Engineering
Quantum field theory predicts a nonlinear response of the vacuum to strong electromagnetic fields of macroscopic extent. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. A particularly distinct signature of the resulting optical activity of the quantum vacuum is vacuum birefringence. This offers an excellent opportunity for a precision test of nonlinear quantum electrodynamics in an uncharted parameter regime. Recently, the operation of the high-intensity Relativistic Laser at the X-ray Free Electron Laser provided by the Helmholtz International Beamline for Extreme Fields has been inaugurated at the High Energy Density scientific instrument of the European X-ray Free Electron Laser. We make the case that this worldwide unique combination of an X-ray free-electron laser and an ultra-intense near-infrared laser together with recent advances in high-precision X-ray polarimetry, refinements of prospective discovery scenarios and progress in their accurate theoretical modelling have set the stage for performing an actual discovery experiment of quantum vacuum nonlinearity.
Sub-picosecond dynamics during relativistic laser-plasma interaction
Autor
M. Almassarani
Erscheinungsjahr
In this dissertation, we explore two major themes related to intense laser-matter interaction. Firstly, we present a comprehensive characterization of the intense THz light and charged particle emission from the rear surface of thin targets during the interaction with ultrashort laser pulses. Secondly, we report the first direct visualization of the Coulomb field of relativistic electron bunches from laser-thin solid interactions on a sub-picosecond timescale. We introduce a novel non-destructive single-shot detection scheme based on the electrooptic principle. Our time-resolved measurements reveal a complex temporal structure with multiple electron bunches propagating at nearly the speed of light. Moreover, our observations confirm the contraction of the electric field of the relativistic electron bunches under the Lorentz transformation. Further, we demonstrate the spatiotemporal evolution of the Coulomb field wavefronts as the electron bunches propagate away from the target. This work paves the way for non-invasive measurements of fast dynamics of charged particles on sub-picosecond timescales.
