17 research outputs found
Strong-field ionization of atoms and molecules with two-color laser pulses
In this work the laser-induced ionization of atoms and simple molecules is experimentally investigated by using a Reaction Microscope and sculpted laser pulses. The Reaction Microscope allows to distinguish different ionization channels with the ion-electron coincidence technique. The sculpted laser pulses, which are realized by superposition of two laser pulses with different colors and adjustable relative phase, play a key role in controlling the electronic wavepacket with high temporal resolution.
With these two methods, phase-controllable strong-field ionization of Ar and N2 is studied and electrons emitted from single ionization of Ar and N2 are compared. Moreover,
channel-selective electron emission is investigated for the fundamental molecular case of H2. A significant difference in the low-energy photoelectron yield between bound and
dissociative ionization channel is observed, proving the Born-Oppenheimer-based two-step process is not complete. Finally, this observation is understood as the population and subsequent decay of autoionizing states by further investigations with the two-color laser pulses
Experimental evidence for Wigner's tunneling time
Tunneling of a particle through a potential barrier remains one of the most
remarkable quantum phenomena. Owing to advances in laser technology, electric
fields comparable to those electrons experience in atoms are readily generated
and open opportunities to dynamically investigate the process of electron
tunneling through the potential barrier formed by the superposition of both
laser and atomic fields. Attosecond-time and angstrom-space resolution of the
strong laser-field technique allow to address fundamental questions related to
tunneling, which are still open and debated: Which time is spent under the
barrier and what momentum is picked up by the particle in the meantime? In this
combined experimental and theoretical study we demonstrate that for
strong-field ionization the leading quantum mechanical Wigner treatment for the
time resolved description of tunneling is valid. We achieve a high sensitivity
on the tunneling barrier and unambiguously isolate its effects by performing a
differential study of two systems with almost identical tunneling geometry.
Moreover, working with a low frequency laser, we essentially limit the
non-adiabaticity of the process as a major source of uncertainty. The agreement
between experiment and theory implies two substantial corrections with respect
to the widely employed quasiclassical treatment: In addition to a non-vanishing
longitudinal momentum along the laser field-direction we provide clear evidence
for a non-zero tunneling time delay. This addresses also the fundamental
question how the transition occurs from the tunnel barrier to free space
classical evolution of the ejected electron.Comment: 31 pages, 15 figures including appendi
Flying doughnut terahertz pulses generated from semiconductor currents
The ability to manipulate the space-time structure of light waves diversifies
light-matter interaction and light-driven applications. Conventionally,
metasurfaces are employed to locally control the amplitude and phase of light
fields by the material response and structure of small meta-atoms. However, the
fixed spatial structures of metasurfaces offer limited opportunities. Here,
using quantum control we introduce a new approach that enables the amplitude,
sign, and even configuration of the generated light fields to be manipulated in
an all-optical manner. Following this approach, we demonstrate the generation
of flying doughnut terahertz (THz) pulses. We show that the single-cycle THz
pulse radiated from the dynamic semiconductor ring current has an electric
field structure that is azimuthally polarized and that the space- and
time-resolved magnetic field has a strong, isolated longitudinal component. As
a first application, we detect absorption features from ambient water vapor on
the spatiotemporal structure of the measured electric fields and the calculated
magnetic fields. Quantum control is a powerful and flexible route to generating
any structured light pulse in the THz range, while pulse compression of
cylindrical vector beams is available for very high-power magnetic-pulse
generation from the mid-infrared to near UV spectral region. Pulses such as
these will serve as unique probes for spectroscopy, imaging,
telecommunications, and magnetic materials
Additional file 1 of Hydrogen alleviated cognitive impairment and blood‒brain barrier damage in sepsis-associated encephalopathy by regulating ABC efflux transporters in a PPARα-dependent manner
Supplementary Material
XUV pump-XUV probe transient absorption spectroscopy at FELs
The emergence of ultra-intense extreme-ultraviolet (XUV) and X-ray free-electron lasers (FELs) has opened the door for the experimental realization of non-linear XUV and X-ray spectroscopy techniques. Here we demonstrate an experimental setup for an all-XUV transient absorption spectroscopy method for gas-phase targets at the FEL. The setup combines a high spectral resolving power of E/ΔE ≈ 1500 with sub-femtosecond interferometric resolution, and covers a broad XUV photon-energy range between approximately 20 and 110 eV. We demonstrate the feasibility of this setup firstly on a neon target. Here, we intensity- and time-resolve key aspects of non-linear XUV-FEL light-matter interactions, namely the non-resonant ionization dynamics and resonant coupling dynamics of bound states, including XUV-induced Stark shifts of energy levels. Secondly, we show that this setup is capable of tracking the XUV-initiated dissociation dynamics of small molecular targets (oxygen and diiodomethane) with site-specific resolution, by measuring the XUV transient absorption spectrum. In general, benefitting from a single-shot detection capability, we show that the setup and method provides single-shot phase-locked XUV pulse pairs. This lays the foundation to perform, in the future, experiments as a function of the XUV interferometric time delay and the relative phase, which enables advanced coherent non-linear spectroscopy schemes in the XUV and X-ray spectral range.ISSN:1359-6640ISSN:1364-549
XUV pump–XUV probe transient absorption spectroscopy at FELs
The emergence of ultra-intense extreme-ultraviolet (XUV) and X-ray free-electron lasers (FELs) has opened the door for the experimental realization of non-linear XUV and X-ray spectroscopy techniques. Here we demonstrate an experimental setup for an all-XUV transient absorption spectroscopy method for gas-phase targets at the FEL. The setup combines a high spectral resolving power of ≈ 1500 with sub-femtosecond interferometric resolution, and covers a broad XUV photon-energy range between approximately 20 and 110 eV. We demonstrate the feasibility of this setup firstly on a neon target. Here, we intensity- and time-resolve key aspects of non-linear XUV-FEL light–matter interactions, namely the non-resonant ionization dynamics and resonant coupling dynamics of bound states, including XUV-induced Stark shifts of energy levels. Secondly, we show that this setup is capable of tracking the XUV-initiated dissociation dynamics of small molecular targets (oxygen and diiodomethane) with site-specific resolution, by measuring the XUV transient absorption spectrum. In general, benefitting from a single-shot detection capability, we show that the setup and method provides single-shot phase-locked XUV pulse pairs. This lays the foundation to perform, in the future, experiments as a function of the XUV interferometric time delay and the relative phase, which enables advanced coherent non-linear spectroscopy schemes in the XUV and X-ray spectral range
XUV-Initiated Dissociation Dynamics of Molecular Oxygen (O)
We performed a time-resolved spectroscopy experixment on the dissociation of oxygen molecules after the interactionwith intense extreme-ultraviolet (XUV) light from the free-electronlaser in Hamburg at Deutsches Elektronen-Synchrotron. Using anXUV-pump/XUV-probe transient-absorption geometry with asplit-and-delay unit, we observe the onset of electronic transitionsin the O cation near 50 eV photon energy, marking the end ofthe progression from a molecule to two isolated atoms. We observetwo different time scales of 290 ± 53 and 180 ± 76 fs for theemergence of different ionic transitions, indicating differentdissociation pathways taken by the departing oxygen atoms.With regard to the emerging opportunities of tuning the centralfrequencies of pump and probe pulses and of increasing the probe−pulse bandwidth, future pump−probe transient-absorptionexperiments are expected to provide a detailed view of the coupled nuclear and electronic dynamics during molecular dissociatio
Nonlinear Coherence Effects in Transient-Absorption Ion Spectroscopy with Stochastic Extreme-Ultraviolet Free-Electron Laser Pulses
We demonstrate time-resolved nonlinear extreme-ultraviolet absorption spectroscopy on multiply charged ions, here applied to the doubly charged neon ion, driven by a phase-locked sequence of two intense free-electron laser pulses. Absorption signatures of resonance lines due to bound–bound transitions between the spin-orbit multiplets and of the transiently produced doubly charged Ne ion are revealed, with time-dependent spectral changes over a time-delay range of (2.4±0.3) fs. Furthermore, we observe 10-meV-scale spectral shifts of these resonances owing to the ac Stark effect. We use a time-dependent quantum model to explain the observations by an enhanced coupling of the ionic quantum states with the partially coherent free-electron laser radiation when the phase-locked pump and probe pulses precisely overlap in time
Measuring the frequency chirp of extreme-ultraviolet free-electron laser pulses by transient absorption spectroscopy
High-intensity ultrashort pulses at extreme ultraviolet (XUV) and x-ray photon energies, delivered by state-of-the-art free-electron lasers (FELs), are revolutionizing the field of ultrafast spectroscopy. For crossing the next frontiers of research, precise, reliable and practical photonic tools for the spectro-temporal characterization of the pulses are becoming steadily more important. Here, we experimentally demonstrate a technique for the direct measurement of the frequency chirp of extreme-ultraviolet free-electron laser pulses based on fundamental nonlinear optics. It is implemented in XUV-only pump-probe transient-absorption geometry and provides in-situ information on the time-energy structure of FEL pulses. Using a rate-equation model for the time-dependent absorbance changes of anionized neon target, we show how the frequency chirp can be directly extracted and quantified from measured data. Since the method does not rely on an additional external field, we expect a widespread implementation at FELs benefiting multiple science fields by in-situ on-target measurement and optimization of FEL-pulse properties