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Publications by
Tobias Helk

All publications of HI Jena


T. Helk, E. Berger, S. Jamnuch, L. Hoffmann, A. Kabacinski, J. Gautier, F. Tissandier, J.-P. Goddet, H.-T. Chang, J. Oh, C. Das Pemmaraju, T. Pascal, S. Sebban, C. Spielmann, and M. Zuerch
Table-top extreme ultraviolet second harmonic generation
Science Advances 7, 2265 (2021)

Abstract: The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties has limited the availability of nonlinear XUV and x-ray spectroscopies to free-electron lasers ( FELs). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source by observing SHG near the TiM2,3 edge with a high-harmonic seeded soft x-ray laser. Furthermore, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and nonresonant contributions. The realization of XUV-SHG on a table-top source opens up more accessible opportunities for the study of element-specific dynamics in multicomponent systems where surface, interfacial, and bulk-phase asymmetries play a driving role.


F. Tuitje, P. Martinez Gil, T. Helk, J. Gautier, F. Tissandier, J. -P. Goddet, A. Guggenmos, U. Kleineberg, S. Sebban, E. Oliva, C. Spielmann, and M. Zuerch
Nonlinear ionization dynamics of hot dense plasma observed in a laser-plasma amplifier
Light: Science & Applications 9, 187 (2020)

Abstract: Understanding the behaviour of matter under conditions of extreme temperature, pressure, density and electromagnetic fields has profound effects on our understanding of cosmologic objects and the formation of the universe. Lacking direct access to such objects, our interpretation of observed data mainly relies on theoretical models. However, such models, which need to encompass nuclear physics, atomic physics and plasma physics over a huge dynamic range in the dimensions of energy and time, can only provide reliable information if we can benchmark them to experiments under well-defined laboratory conditions. Due to the plethora of effects occurring in this kind of highly excited matter, characterizing isolated dynamics or obtaining direct insight remains challenging. High-density plasmas are turbulent and opaque for radiation below the plasma frequency and allow only near-surface insight into ionization processes with visible wavelengths. Here, the output of a high-harmonic seeded laser-plasma amplifier using eight-fold ionized krypton as the gain medium operating at a 32.8 nm wavelength is ptychographically imaged. A complex-valued wavefront is observed in the extreme ultraviolet (XUV) beam with high resolution. Ab initio spatio-temporal Maxwell-Bloch simulations show excellent agreement with the experimental observations, revealing overionization of krypton in the plasma channel due to nonlinear laser-plasma interactions, successfully validating this four-dimensional multiscale model. This constitutes the first experimental observation of the laser ion abundance reshaping a laser-plasma amplifier. The presented approach shows the possibility of directly modelling light-plasma interactions in extreme conditions, such as those present during the early times of the universe, with direct experimental verification.

F. Tuitje, M. Zürch, T. Helk, J. Gautier, F. Tissandier, J.-P. Goddet, E. Oliva, A. Guggenmos, U. Kleineberg, H. Stiel, S. Sebban, and C. Spielmann
Ptychography and single-shot nanoscale imaging with plasma-based laser sources
Springer Proceedings in Physics 241, 155 (2020)

Abstract: We report the direct wavefront characterization of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength and monitor the exit of the laser plasma amplifier depending on the arrival time of the seed pulses with respect to pump pulses. For the wavefront measurement in phase and intensity, we used high-resolution ptychography. After propagating the wavefront back to the source, we are able to observe the rear end of the plasma amplifier. We compare the characteristics of the seeded soft X-ray Laser to an unseeded one and find an increasing beam stability and lateral coherence important for lensless imaging techniques.


F. Tuitje, T. Helk, M. Zürch, and C. Spielmann
Extreme ultraviolet lensless imaging of biological specimen
Proceedings of SPIE 10890, 80 (2019)

Abstract: Imaging of biological specimen is one of the most important tools to investigate structures and functionalities in organic components. Improving the resolution of images into the nanometer range call for short wavelengths light sources and large aperture optics. Subsequently, the use of extreme ultraviolet light in the range of 2 nm to 5 nm provides high contrast and high resolution imaging, if it is combined with lensless imaging techniques. We describe important parameters for high resolution lensless imaging of biological samples and specify the required light source properties. To overcome radiation based damage of biological specimen, we discuss the concept of ghost imaging and describe a possible setup towards biological imaging in the extreme ultraviolet range.

F. Tuitje, T. Helk, M. Zürch, J. Gautier, F. Tissandier, J.-P. Goddet, E. Oliva, A. Guggenmos, U. Kleineberg, S. Sebban, and C. Spielmann
Following the plasma dynamics in a seeded soft x-ray laser with lensless imaging
Proceedings of SPIE 10903, 9 (2019)

Abstract: We evaluated the capabilities of an intense ultrafast high-harmonic seeded soft X-ray laser at 32.8 nm wavelength regarding single-shot lensless imaging and ptychography. Additionally the wave front at the exit of the laser plasma amplifier is monitored in amplitude and phase using high resolution ptychography and backpropagation techniques.Characterizing the laser plasma amplifier performance depending on the arrival time of the seed pulse with respect to pump pulses provides insight into the light plasma interaction in the soft X-ray range.

T. Helk, M. Zürch, and C. Spielmann
Perspective: Towards single shot time-resolved microscopy using short wavelength table-top light sources
Structural Dynamics 6, 010902 (2019)

Abstract: Time-resolved imaging allows revealing the interaction mechanisms in the microcosm of both inorganic and biological objects. While X-ray microscopy has proven its advantages for resolving objects beyond what can be achieved using optical microscopes, dynamic studies using full-field imaging at the nanometer scale are still in their infancy. In this perspective, we present the current state of the art techniques for full-field imaging in the extreme-ultraviolet- and soft X-ray-regime which are suitable for single exposure applications as they are paramount for studying dynamics in nanoscale systems. We evaluate the performance of currently available table-top sources, with special emphasis on applications, photon flux, and coherence. Examples for applications of single shot imaging in physics, biology, and industrial applications are discussed.

M. Zuerch, F. Tuitjea, T. Helk, J. Gautier, F. Tissandier, J. -P. Goddet, E. Oliva, A. Guggenmos, U. Kleineberg, H. Stiel, S. Sebban, and C. Spielmann
Lab-scale soft X-ray ptychography: advanced nanoscale imaging and beam diagnostics
No abstract availableLinkBibTeX
M. Zuerch, F. Tuitje, T. Helk, J. Gautier, F. Tissandier, J.-P. Goddet, A. Guggenmos, U. Kleineberg, S. Sebban, and C. Spielmann
Single shot XUV nanoimaging using an intense femtosecond soft X-ray laser
No abstract availableLinkBibTeX