Auger electron wave packet interferometry on extreme timescales with coherent soft x-rays
S. Usenko et al.
Wave packet interferometry provides benchmark information on light-induced electronic quantum states by monitoring their relative amplitudes and phases during coherent excitation, propagation, and decay. The relative phase control of soft x-ray pulse replicas on the single-digit attosecond timescale achieved in our experiments makes this method a powerful tool to probe ultrafast quantum phenomena such as the excitation of Auger shake-up states with sub-cycle precision. In this contribution we present first results obtained for different Auger decay channels upon generating L-shell vacancies in argon atoms using Michelson-type all-reflective interferometric autocorrelation at a central free-electron laser photon energy of 274.7 eV.
Shaping femtosecond laser pulses at short wavelength with grazing-incidence optics
L. L. Lazzarino, M. M. Kazemi, C. Haunhorst, C. Becker, S. Hartwell, M. A. Jakob, A. Przystawik, S. Usenko, D. Kip, I. Hartl, and T. Laarmann
We present the design of an extreme ultraviolet (XUV) pulse shaper relying on reflective optics. The instrument will allow tailoring of the time-frequency spectrum of femtosecond pulses generated by seeded free-electron lasers (FEL) and high-harmonic generation (HHG) sources down to a central wavelength of ~15 nm. The device is based on the geometry of a 4f grating compressor that is a standard concept in ultrafast laser science and technology. We apply it to shorter wavelengths using grazing-incidence optics operated under ultra-high vacuum conditions. The design blaze angle and the line density of the gratings allow the manipulation of all different harmonics typical for seeded FEL and HHG photon sources without the need of realignment of the instrument and even simultaneously in multi-color experiments. A proof-of-principle pulse shaping experiment using 266 nm laser light has been performed, demonstrating relative phase-control of femtosecond UV pulses.
VUV-induced dynamics of the electronically excited C2D4 molecule in a single-color pump-probe experiment
Oliver Schepp, Arne Baumann, Marek Wieland, Armin Azima, Markus Drescher
The ultrafast non-adiabatic dynamics of the electronically excited ethylene molecule C2H4 and its deuterated isotopologue C2D4 are studied with time-resolved photoelectron spectroscopy after excitation via irradiation with light in the vacuum ultraviolet spectral range. Sub-20-fs pulses, generated as the fifth harmonic of a Ti:Sa laser system, are split and delayed in an all-reflective Michelson-type interferometer, enabling a single-color pump-probe experiment. In addition to the ultrafast non-adiabatic relaxation process of C2H4, we find more complex dynamics exhibited by the delay-dependent photoelectron yield of C2D4, identified as a signature of the delayed dissociative ionization of the parent ion.
Chemical Physics Letters: X, Volume 3, 1000024 (2019);
Time-Resolved Dissociation Dynamics of Iodomethane Resulting from Rydberg and Valence Excitation
Arne Baumann, Dimitrios Rompotis, Oliver Schepp, Marek Wieland, and Markus Drescher
Rydberg excitations in the vacuum ultraviolet spectral range may open up molecular photoreaction pathways not accessible from lower-lying valence states. Here, single-shot UV/VUV pump–probe spectroscopy was used to study the photodissociation dynamics of iodomethane after 268 nm excitation in the A-band and excitation of the 6p (2E3/2) Rydberg state at 161 nm. By combining weak-field VUV single-photon ionization with sub-10 fs temporal resolution and the superior statistical accuracy of the single-shot technique, sub-30 fs wave packet dynamics upon excitation in the A-band by a UV pump pulse were disclosed. Population transfer from the Rydberg state to the 2 1A1 valence state leading to 100 fs dissociation dynamics was observed by utilizing the same methodology in a VUV-pump/UV-probe scheme.
J. Phys. Chem. A, 2018, 122 (21), pp 4779–4784
Weak-field few-femtosecond VUV photodissociation dynamics of water isotopologues
A. Baumann, S. Bazzi, D. Rompotis, O. Schepp, A. Azima, M. Wieland, D. Popova-Gorelova, O. Vendrell, R. Santra, M. Drescher
We present a joint experimental and theoretical study of the VUV-induced dynamics of H2O and its deuterated isotopologues in the first excited state (˜A1B1) utilizing a VUV-pump VUV-probe scheme combined with ab initio classical trajectory calculations. 16-fs VUV pulses centered at 161 nm created by fifth-order harmonic generation are employed for single-shot pump-probe measurements. Combined with a precise determination of the VUV pulses' temporal profile, they provide the necessary temporal resolution to elucidate sub-10-fs dissociation dynamics in the 1+1 photon ionization time window. Ionization with a single VUV photon complements established strong-field ionization schemes by disclosing the molecular dynamics under perturbative conditions. Kinetic isotope effects derived from the pump-probe experiment are found to be in agreement with our by ab initio classical trajectory calculations, taking into account photoionization cross sections for the ground and first excited state of the water cation.
Single-shot nonlinear spectroscopy in the vacuum-ultraviolet
D. Rompotis, A. Baumann, O. Schepp, T. Maltezopoulos, M. Wieland, M. Drescher
Time-resolved spectroscopy in the vacuum/extreme ultraviolet (VUV/XUV) spectral range promises to disclose ultrafast dynamics in all states of matter. Completing a measurement within a single shot eliminates the influence of experimental parameter fluctuations and enhances its statistical significance. We demonstrate a single-shot temporal metrology scheme operating in the vacuum/extreme-ultraviolet spectral range, combining few-femtosecond resolution in a wide temporal window with high detection efficiency. An anticollinear geometry encodes temporal delay information on the beam propagation coordinate. The spatial distribution of ions created in the common focus is captured with a mass/charge-state-selective ion imaging spectrometer, resulting in a single-shot pump–probe measurement. We demonstrate a proof-of-principle single-shot VUV-pump/VUV-probe experiment by investigating ultrafast dissociation dynamics of O2 excited at 162 nm. The experimental determination of the finite instrument response in the same apparatus enables robust deconvolution of the investigated dynamics well beyond the instrument’s intrinsic temporal resolution.
Optica Vol. 4, Issue 8, pp. 871-878 (2017)
Attosecond interferometry with self-amplified spontaneous emission of a free-electron laser
Usenko, A. Przystawik, M.A. Jakob, L.L. Lazzarino, G. Brenner, S. Toleikis, Ch. Haunhorst, D. Kip, T. Laarmann
Light-phase-sensitive techniques, such as coherent multidimensional spectroscopy, are well-established in a broad spectral range, already spanning from radio-frequencies in nuclear magnetic resonance spectroscopy to visible and ultraviolet wavelengths in nonlinear optics with table-top lasers. In these cases, the ability to tailor the phases of electromagnetic waves with high precision is essential. Here we achieve phase control of extreme-ultraviolet pulses from a free-electron laser (FEL) on the attosecond timescale in a Michelson-type all-reflective interferometric autocorrelator. By varying the relative phase of the generated pulse replicas with sub-cycle precision we observe the field interference, that is, the light-wave oscillation with a period of 129 as. The successful transfer of a powerful optical method towards short-wavelength FEL science and technology paves the way towards utilization of advanced nonlinear methodologies even at partially coherent soft X-ray FEL sources that rely on self-amplified spontaneous emission.
Split-and-delay unit for FEL interferometry in the XUV spectral range
S. Usenko, A. Przystawik, L.L. Lazzarino, M.A. Jakob, F. Jacobs, C. Becker, C. Haunhorst, D. Kip, and T. Laarmann
In this work we present a reflective split-and-delay unit (SDU) developed for interferometric time-resolved experiments utilizing an (extreme ultraviolet) XUV pump–XUV probe scheme with focused free-electron laser beams. The developed SDU overcomes limitations for phase-resolved measurements inherent to conventional two-element split mirrors by a special design using two reflective lamellar gratings. The gratings produce a high-contrast interference signal controlled by the grating displacement in every diffraction order. The orders are separated in the focal plane of the focusing optics, which enables one to avoid phase averaging by spatially selective detection of a single interference state of the two light fields. Interferometry requires a precise relative phase control of the light fields, which presents a challenge at short wavelengths. In our setup the phase delay is determined by an in-vacuum white light interferometer (WLI) that monitors the surface profile of the SDU in real time and thus measures the delay for each laser shot. The precision of the WLI is 1 nm as determined by optical laser interferometry. In the presented experimental geometry it corresponds to a time delay accuracy of 3 as, which enables phase-resolved XUV pump–XUV probe experiments at free-electron laser (FEL) repetition rates up to 60 Hz.
Appl. Sci. 7, 544 (2017)
Femtosecond dynamics of correlated many-body states in C60 fullerenes
S. Usenko, M. Schüler, A. Azima, M. Jakob, L.L. Lazzarino, Y. Pavlyukh, A. Przystawik, M. Drescher, T. Laarmann, J. Berakdar
Fullerene complexes may play a key role in the design of future molecular electronics and nanostructured devices with potential applications in light harvesting using organic solar cells. Charge and energy flow in these systems is mediated by many-body effects. We studied the structure and dynamics of laser-induced multi-electron excitations in isolated C60 by two-photon photoionization as a function of excitation wavelength using a tunable fs UV laser and developed a corresponding theoretical framework on the basis of ab initio calculations. The measured resonance line width gives direct information on the excited state lifetime. From the spectral deconvolution we derive a lower limit for purely electronic relaxation on the order of Tel=10+5-3 fs. Energy dissipation towards nuclear degrees of freedom is studied with time-resolved techniques. The evaluation of the nonlinear autocorrelation trace gives a characteristic time constant of Tvib=400+-100 fs for the exponential decay. In line with the experiment, the observed transient dynamics is explained theoretically by nonadiabatic (vibronic) couplings involving the correlated electronic, the nuclear degrees of freedom (accounting for the Herzberg–Teller coupling), and their interplay.
New J. Phys. 18, 113055 (2016)
Tracing few-femtosecond photodissociation dynamics on molecular oxygen with a single-color pump-probe scheme in the VUV
O. Schepp, A. Baumann, D. Rompotis, T. Gebert, A. Azima, M. Wieland, M. Drescher
Phys. Rev. A 94, 033411 – Published 13 September 2016
Efficient generation of below-threshold harmonics for high-fidelity multi-photon physics in the VUV spectral range
D. Rompotis, T. Gebert, M. Wieland, F. Karimi, M. Drescher
We demonstrate the generation of microjoule level, sub-20-fs, Ti:Sa fifth-harmonic pulses utilizing a loose-focusing geometry in a long Ar gas cell. The VUV pulses centered at 161.8 nm reach pulse energies of 1.1 μJ per pulse, while the corresponding pulse duration is measured with a second-order, fringe-resolved autocorrelation scheme to be 18±1 fs. Nonresonant, two-photon ionization of Kr and three-photon ionization of Ne verify the fifth-harmonic pulse high-intensity content and indicate the feasibility of multi-photon VUV pump-VUV probe studies of ultrafast atomic and molecular dynamics.
Optics Letters Vol. 40, 1675-1678
Ionisation dynamics of Xe nanoplasma formation studied with XUV fluorescence spectroscopy
A. Przystawik, L. Schroedter, M. Müller, M. Adolph, C. Bostedt, L. Flückiger, T. Gorkhover, A. Kickermann, M. Krikunova, Nösel, T. Oelze, Y. Ovcharenko, D. Rupp, L. M. Sauppe, S. Schorb, S. Usenko, T. Möller, T. Laarmann
Intense pulses from a short wavelength free-electron laser turn xenon nanoparticles into a high energy density nanoplasma within femtoseconds. Recently, the generation of multiply charged xenon ions during the initial phase of plasma evolution has been studied by energy-resolved XUV fluorescence detection as a function of cluster size and cluster composition . In the present contribution we give a detailed analysis of the corresponding radiative transitions after resonant excitation of the 4d electron shell at intensities of 2 × 1012 − 2.45 × 1015 W cm−2. The evaluation of charge-state specific fluorescence yields as a function of FEL power density demonstrates that plasma effects such as ionization potential lowering, electron impact excitation, ionization, and energy redistribution govern the laser-induced non-equilibrium dynamics in xenon clusters.
Journal of Physics B 48, 184002
Ionization dynamics of XUV excited clusters: the role of inelastic electron collisions
M. Müller, L. Schroedter, T. Oelze, L. Nösel, A. Przystawik, A. Kickermann, M. Adolph, T. Gorkhover, L. Flückiger, M. Krikunova, M. Sauppe, Y. Ovcharenko, S. Schorb, C. Bostedt, D. Rupp, T. Laarmann, T. Möller
We report on the ionization and nanoplasma dynamics of small xenon clusters irradiated by intense, short pulses of a short-wavelength free-electron laser. Fluorescence spectroscopy indicates that inelastic electron collisions play a prominent role in the formation of the highest charge states. From the spectral distribution an electron temperature of 27 eV is deduced which corresponds to the average excess energy of the Auger- and photoelectrons ionized from individual atoms but trapped in the cluster core. This suggests that fluorescence spectra reflect a very early stage within the nanoplasma dynamics and shows how a part of the kinetic energy of the plasma electrons trapped in the cluster potential is transferred to the ions.
Journal of Physics B 48, 174002
Hidden Charge States in Soft-X-Ray Laser-Produced Nanoplasmas Revealed by Fluorescence Spectroscopy
L. Schroedter, M. Müller, A. Kickermann, A. Przystawik, S. Toleikis, M. Adolph, L. Flückiger, T. Gorkhover, L. Nösel, M. Krikunova, T. Oelze, Y. Ovcharenko, D. Rupp, M. Sauppe, D. Wolter, S. Schorb, C. Bostedt, T. Möller, T. Laarmann
Highly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least.
Phys. Rev. Lett. 112, 183401 (2014)
A high-harmonic generation source for seeding a free-electron laser at 38 nm
T. Maltezopoulos, M. Mittenzwey, A. Azima, J. Bödewadt, H. Dachraoui, M. Rehders, C. Lechner, M. Schulz, M. Wieland, T. Laarmann, J. Roßbach, M. Drescher
Direct seeding with a high-harmonic generation (HHG) source can improve the spectral, temporal, and coherence properties of a free-electron laser (FEL) and shall reduce intensity and arrival-time fluctuations. In the seeding experiment sFLASH at the extreme ultraviolet FEL in Hamburg FLASH, which operates in the self-amplified spontaneous emission mode (SASE), the 21st harmonic of an 800 nm laser is refocused into a dedicated seeding undulator. For seeding, the external light field has to overcome the noise level of SASE; therefore, an efficient coupling between seed pulse and electron bunch is mandatory. Thus, an HHG beam with a proper divergence, width, beam quality, Rayleigh length, pointing stability, single-shot pulse energy, and stability in the 21st harmonic is needed. Here, we present the setup of the HHG source that seeds sFLASH at 38.1 nm, the optimization procedures, and the necessary diagnostics.
Applied Physics B, Volume 115, Issue 1, pp 45-54 (2014)
Generation of the simplest rotational wave packet in a diatomic molecule: Tracing a two-level superposition in the time domain
A. Przystawik, A. Kickermann, A. Al-Shemmary, S. Düsterer, A. M. Ellis, K. von Haeften, M. Harmand, S. Ramakrishna, H. Redlin, L. Schroedter, M. Schulz, T. Seideman, N. Stojanovic, J. Szekely, F. Tavella, S. Toleikis, T. Laarmann
We introduce a time-domain approach to explore rotational dynamics caused by intramolecular coupling or the interaction with dissipative media. It pushes the time resolution toward the ultimate limit determined by the rotational period. Femtosecond pulses create a coherent superposition of two rotational states of carbon monoxide. The wave-packet motion is observed by subsequent Coulomb explosion, which results in a time-dependent asymmetry of spatial fragmentation patterns. The asymmetry oscillation prevails for at least 1 ns, covering more than 300 periods with no decoherence. Long time scans will allow weak perturbations of the order of ΔE/E=10−4 to be discerned. Our conclusions are confirmed by a fully quantum-mechanical model.
Phys. Rev. A 85, 052503 (2012)
Michelson-type all-reflective interferometric autocorrelation in the VUV regime
T. Gebert, D. Rompotis, M. Wieland, F. Karimi, A. Azima, M. Drescher
We demonstrate second-order interferometric autocorrelation of a pulse in the vacuum-ultraviolet (VUV) spectral range using an optical arrangement equivalent to a Michelson interferometer. In an all-reflective design, wavefront splitting is realized with two moveable interdigitated reflective gratings forming a diffraction pattern with well separated orders and an intensity distribution depending on the precisely adjustable path-length difference. An imaging time-of-flight spectrometer is able to spatially select ions created by nonlinear two-photon absorption in the focus of the zeroth diffraction order. This arrangement is used to demonstrate interferometric autocorrelation in krypton with femtosecond VUV pulses at 160 nm wavelength. In addition to the pulse duration, which is already accessible with non-collinear intensity autocorrelation, the full interferometric contrast of the presented approach enables us to extract also information on temporal phases.
Int. J. Opt. 2011, 417075 (2011)