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Publications by
Dr. Michael Zürch

All publications of HI Jena


R. Hollinger, P. Herrmann, V. Korolev, M. Zapf, V. Shumakova, R. Roeder, I. Uschmann, A. Pugzlys, A. Baltuska, M. Zurch, C. Ronning, C. Spielmann, and D. Kartashov
Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO
Nanomaterials 11, 4 (2021)

Abstract: The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this work we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3-4 mu m. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.

R. Hollinger, E. Haddad, M. Zapf, V. Shumakova, P. Herrmann, R. Roder, I. Uschmann, U. Reislohner, A. Pugzlys, A. Baltuska, F. Legare, M. Zurch, C. Ronning, C. Spielmann, and D. Kartashov
Contribution of free carriers to light absorption upon intense light-semiconductor interaction

Abstract: In this work we investigated the role of free carriers in the interaction of a wide-band gap semiconductor with strong light fields at long wavelengths. Motivated by the beneficial scaling law of the pondermotive potential (U p ~ Iλ 2 ), the interaction of intense long wavelength laser pulses with condensed matter has attracted huge attention over the last decade [Kruchinin] . After excitation of quasi free electrons in the conduction band (CB) via multiphoton absorption or tunnelling the strong pondermotive force leads to highly energetic free electrons. Bound electrons can be collisionally excited if the energy of the free electrons exceed the band gap energy. Here, we use the onset of near ultraviolet (NUV) stimulated emission in ZnO thin films ( Fig. 1a ) to study off-resonance light absorption and the role of free carriers thereby.

P. Herrmann, R. Hollinger, V. Korolev, M. Zapf, V. Shumakova, R. Roder, I. Uschmann, A. Pugzlys, A. Baltuska, M. Zurch, C. Ronning, C. Spielmann, and D. Kartashov
Ellipticity dependent excitation and high harmonic generation from intense mid-IR laser pulses in ZnO

Abstract: In this contribution we experimental examine the ellipticity dependence of strong off resonance absorption and high harmonic generation (HHG) in the wide band gap semiconductor ZnO upon irradiation with intense mid-IR laser pulses. HHG in semiconductors originates from nonlinear intraband currents and interband transitions of the electrons driven by the strong mid-IR fields [Ghimire]. Here, we show that the intra- and interband contribution to HHG in a ZnO thin film are affected differently by the driving laser ellipticity.

T. Helk, E. Berger, L. Hoffmann, A. Kabacinski, J. Gautier, F. Tissandier, J. P. Goddet, S. Sebban, C. Spielmann, and M. Zurch
Extreme Ultraviolet Second Harmonic Generation using a seeded soft X-ray laser

Abstract: Non-linear interactions between light and matter are crucial for widespread applications in physical sciences, life science and engineering. Second harmonic generation (SHG) and sum-frequency generation spectroscopy in the near infrared and optical range have enabled intriguing insights into surface properties and how they influence for instance chemical reactions [1] . Expansion of these methods by developing non-linear X-ray spectroscopies has recently added the capability of studying surfaces [2] , symmetry-breaking [3] and buried interfaces [4] with elemental specificity. However, widespread application is currently limited by access to free-electron laser facilities. Here we report the first generation of second harmonic emission in the extreme ultraviolet (XUV-SHG) at the titanium M-edge. The experiments were carried out with a high-harmonic seeded SXRL [5] bringing nonlinear XUV spectroscopy with atomic specificity to the table-top. The SXRL pulses with an energy of (14 ± 2) nJ, a pulse duration of (1.73 ± 0.13) ps, wavelength of 32.8 nm and a Gaussian-like beam profile is focused down with a gold ellipsoidal mirror down to an elliptical spot with a size of roughly 20 µ m x 40 µ m. The estimated intensity on target is about of (1.0 ± 0.1)•10 10 W/cm 2 . In the focus we exceeded the damage threshold fluence of 2 mJ/cm 2 and observed single-shot damage of 50 nm Ti foils. At these intensities we also generate second harmonic light at 75.6 eV. The fundamental and SHG beams are refocused with a toroidal mirror, spectrally separated by a grating and imaged on a cooled CCD camera.

R. Hollinger, N. Harshitha, V. Korolev, Z. Gan, A. George, V. Shumakova, M. Zürch, T. Vogl, A. P. zlys, A. B. ska, F. Eilenberger, C. Spielmann, A. Turchanin, and D. Kartashov
Ellipticity controlled high-order harmonic generation in 2D materials

Abstract: High harmonic generation (HHG) in a single-atomic-layer non-centrosymmetric semiconductor is investigated experimentally for different driving laser field polarizations. The ellipticity enhanced even-order HHG for certain crystal orientations reveals linked laser and valley polarizations.


N. Geib, R. Hollinger, E. Haddad, P. Herrmann, F. Légaré, T. Pertsch, C. Spielmann, M. Zürch, and F. Eilenberger
Discrete dispersion scan setup for measuring few-cycle laser pulses in the mid-infrared
Optics Letters 45, 5295 (2020)

Abstract: In this work, we demonstrate a discrete dispersion scan scheme using a low number of flat windows to vary the dispersion of laser pulses in discrete steps. Monte Carlo simulations indicate that the pulse duration can be retrieved accurately with less than 10 dispersion steps, which we verify experimentally by measuring few-cycle pulses and material dispersion curves at 3 and 10 µm wavelength. This minimal measuring scheme using only five optical components without the need for linear positioners and interferometric alignment can be readily implemented in many wavelength ranges and situations.

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.

G. Tadesse, W. Eschen, R. Klas, M. Tschernajew, T. Frederik, M. Steinert, M. Zilk, V. Schuster, M. Zürch, T. Pertsch, C. Spielmann, J. Limpert, and J. Rothhardt
Wavelength-scale ptychographic coherent diffractive imaging using a high-order harmonic source
Scientific Reports 9, 1735 (2019)

Abstract: Ptychography enables coherent diffractive imaging (CDI) of extended samples by raster scanning across the illuminating XUV/X-ray beam, thereby generalizing the unique advantages of CDI techniques. Table- top realizations of this method are urgently needed for many applications in sciences and industry. Previously, it was only possible to image features much larger than the illuminating wavelength with table-top ptychography although knife-edge tests suggested sub-wavelength resolution. However, most real-world imaging applications require resolving of the smallest and closely-spaced features of a sample in an extended field of view. In this work, resolving features as small as 2.5 \lambda (45 nm) using a table-top ptychography setup is demonstrated by employing a high-order harmonic XUV source with record-high photon flux. For the first time, a Rayleigh-type criterion is used as a direct and unambiguous resolution metric for high-resolution table-top setup. This reliably qualifies this imaging system for real-world applications e.g. in biological sciences, material sciences, imaging integrated circuits and semiconductor mask inspection.

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. Zurch, A. Guggenmos, R. Jung, J. Rothhardt, C. Spath, J. Tümmler, S. Demmler, S. Haedrich, J. Limpert, A. Tünnermann, U. Kleineberg, H. Stiel, and C. Spielmann
Coherent Diffraction Imaging with Tabletop XUV Sources

Abstract: Coherent diffraction imaging (CDI) at wavelengths in the extreme ultraviolet range has become an important tool for nanoscale investigations. Employing laser-driven high harmonic sources allows for lab-scale applications such as cancer cell classification and phase-resolved surface studies in reflection geometry. The excellent beam properties support a spatial resolution below the wavelength, i.e., close to the Abbe limit. Unfortunately, the usually low photon flux of HHG sources limits their applicability. Recent advances in ultrafast fiber laser development cumulated in sources delivering average powers approaching the milliwatt level in the extreme ultraviolet. In comparison, a tabletop soft X-ray laser driven by moderate pump energies was recently employed for CDI featuring excellent temporal coherence and extraordinary high flux allowing for single-shot imaging.


R. Sollapur, D. Kartashov, M. Zürch, A. Hoffmann, T. Grigorova, G. Sauer, A. Hartung, A. Schwuchow, J. Bierlich, J. Kobelke, M. Chemnitz, M. A. Schmidt, and C. Spielmann
Resonance-enhanced multi-octave supercontinuum generation in antiresonant hollow-core fibers
Light: Science & Applications 6, e17124 (2017)

Abstract: Ultrafast supercontinuum generation in gas-filled waveguides is an enabling technology for many intriguing applications ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. In this study, we show that structural resonances in a gas-filled antiresonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, which enables the generation of more than three octaves of broadband light that ranges from deep UV wavelengths to near infrared. Our observation relies on the introduction of a geometric-induced resonance in the spectral vicinity of the ultrafast pump laser, outperforming gas dispersion and yielding a unique dispersion profile independent of core size, which is highly relevant for scaling input powers. Using a krypton-filled fiber, we observe spectral broadening from 200 nm to 1.7 μm at an output energy of ∼ 23 μJ within a single optical mode across the entire spectral bandwidth. Simulations show that the frequency generation results from an accelerated fission process of soliton-like waveforms in a non-adiabatic dispersion regime associated with the emission of multiple phase-matched Cherenkov radiations on both sides of the resonance. This effect, along with the dispersion tuning and scaling capabilities of the fiber geometry, enables coherent ultra-broadband and high-energy sources, which range from the UV to the mid‐infrared spectral range.

M. Zürch, R. Jung, C. Späth, J. Tümmler, A. Guggenmos, D. Attwood, U. Kleineberg, H. Stiel, and C. Spielmann
Transverse Coherence Limited Coherent Diffraction Imaging using a Molybdenum Soft X-ray Laser Pumped at Moderate Pump Energies
Scientific Reports 7, 5314 (2017)

Abstract: Coherent diffraction imaging (CDI) in the extreme ultraviolet has become an important tool for nanoscale investigations. Laser-driven high harmonic generation (HHG) sources allow for lab scale applications such as cancer cell classification and phase-resolved surface studies. HHG sources exhibit excellent coherence but limited photon flux due poor conversion efficiency. In contrast, table-top soft X-ray lasers (SXRL) feature excellent temporal coherence and extraordinary high flux at limited transverse coherence. Here, the performance of a SXRL pumped at moderate pump energies is evaluated for CDI and compared to a HHG source. For CDI, a lower bound for the required mutual coherence factor of |μ12| ≥ 0.75 is found by comparing a reconstruction with fixed support to a conventional characterization using double slits. A comparison of the captured diffraction signals suggests that SXRLs have the potential for imaging micron scale objects with sub-20 nm resolution in orders of magnitude shorter integration time compared to a conventional HHG source. Here, the low transverse coherence diameter limits the resolution to approximately 180 nm. The extraordinary high photon flux per laser shot, scalability towards higher repetition rate and capability of seeding with a high harmonic source opens a route for higher performance nanoscale imaging systems based on SXRLs.