Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates

We report on a newly built laser based tabletop setup which enables generation of femtosecond light pulses in the XUV range via employing the process of high order harmonic generation HHG in a gas medium. The spatial, spectral, and temporal characteristics of the XUV beam are presented. Monochromatization of XUV light with minimum temporal pulse distortion is the central issue of this work. Off center reflection zone plates are shown to be superior to gratings when selection of a desired harmonic is carried out with the use of a single optical element. A cross correlation technique was applied to characterize the performance of zone plates in the time domain. By using laser pulses of 25 fs length to pump the HHG process, a pulse duration of 45 fs for monochromatized harmonics was achieved in the present setu

Light-induced relaxation dynamics of the ferricyanide ion revisited by ultrafast XUV photoelectron spectroscopy

Photoinduced charge transfer in transition-metal coordination complexes plays a prominent role in photosynthesis and is fundamental for light-harvesting processes in catalytic materials. However, revealing the relaxation pathways of charge separation remains a very challenging task because of the complexity of relaxation channels and ultrashort time scales. Here, we employ ultrafast XUV photoemission spectroscopy to monitor fine mechanistic details of the electron dynamics following optical ligand-to-metal charge-transfer excitation of ferricyanide in aqueous solution. XUV probe light with a time resolution of 100 fs, in combination with density functional theory employing the Dyson orbital formalism, enabled us to decipher the primary and subsequently populated electronic states involved in the relaxation, as well as their energetics on sub-picosecond timescales. We find strong evidence for the spin crossover followed by geometrical distortions due to vibronic interactions (Jahn–Teller effect) in the excited electronic states, rather than localization/delocalization dynamics, as suggested previously

Laser assisted electron scattering in strong field ionization of dense water vapor by few cycle laser pulses

We report on strong field ionization of dense water gas in a short laser pulse of a few optical cycles. By employing a unique combination of photoelectron spectroscopy with a liquid micro jet technique, we observe how the character of electron emission at high kinetic energies changes with the increase of the gas density. This change is associated with the process of laser assisted electron scattering LAES on neighboring particles, which becomes a dominant mechanism of hot electron emission at higher medium densities. The manifestation of this mechanism is found to require densities which are orders of magnitude lower than those considered for heating of laser generated plasmas via the LAES process. The experimental results are supported by simulations of the LAES yield with the use of the Kroll Watson theor

Laser-assisted electron scattering in strong-field ionization of dense water vapor by ultrashort laser pulses

Photograph used for a story in the Daily Oklahoman newspaper. Caption: "Towering spray of gas and distillate roared up the center of the derrick at the Hall-Jones No. 1 Scott Unit Monday near Canton, shortly before the wild wildcat was brought under control. The well, near one that burned 10 months before it was extinguished in June, blew out Sunday.

Ultrafast spin crossover in [FeII bpy 3]2 revealing two competing mechanisms by means of XUV photoemission spectroscopy

Photoinduced spin flip in FeII complexes is an ultrafast phenomenon that has the potential to become an alternative to conventional processing and magnetic storage of information. Following the initial excitation by visible light into the singlet metal to ligand charge transfer state, the electronic transition to the high spin quintet state may undergo different pathways. Here we apply ultrafast XUV photoemission spectroscopy to track the low to high spin dynamics in the aqueous iron tris bipyridine complex, [Fe bpy 3]2 , by monitoring the transient electron density distribution among excited states with a femtosecond time resolution. Aided by first principles calculations, this approach enables to reveal unambiguously both the sequential and direct de excitation pathways from singlet to quintet state, with a branching ratio of 4.5 1

Ultrafast photoelectron spectroscopy of solutions space charge effect

The method of time resolved XUV photoelectron spectroscopy is applied in a pump probeexperiment on a liquid micro jet. We investigate how the XUV energy spectra of photoelectrons are influenced by the space charge created due to ionization of the liquid medium by the pump laser pulse. XUV light from high order harmonic generation is used to probe the electron population of the valence shell of iron hexacyanide in water. By exposing the sample to a short UV pump pulse of 266 nm wavelength and amp; 8764;55 fs duration, we observe an energy shift of the spectral component associated with XUV ionization from the Fe 3d t2g orbital as well as a shift of the water spectrum. Depending on the sequence of the pump and probe pulses, the arising energy shift of photoelectrons acquires a positive or negative value. It exhibits a sharp positive peak at small time delays, which facilitates to determine the temporal overlap between pump and probe pulses. The negative spectral shift is due to positive charge accumulated in the liquid medium during ionization. Its dissipation is found to occur on a sub nanosecond time scale and has a biexponential character. A simple mean field model is provided to interpret the observations. A comparison between the intensity dependencies of the spectral shift and the UV ionization yield shows that the space charge effect can be significantly reduced when the pump intensity is attenuated below the saturation level of water ionization. For the given experimental conditions, the saturation intensity lies at 6x1010 Wcm amp; 8722;2

Anti-native and recombinant myeloperoxidase monoclonals and human autoantibodies

Myeloperoxidase (MPO) is one of the main antigen targets of anti-neutrophil cytoplasmic antibodies (ANCA) in systemic vasculitides. It has been suggested that anti-MPO antibodies may recognize a single epitope on recombinant MPO. If confirmed on native MPO, this might allow specific therapeutic intervention with anti-idiotypic MoAbs to prevent antibody–antigen interaction which is thought to cause activation of neutrophils and vasculitis. We searched for restriction in the epitope recognition profile in 50 patients with anti-MPO autoantibodies, using both native and recombinant MPO. Mouse monoclonals were purified and tested in competition assays. At least four epitopes were identified on native MPO using these monoclonals and only two were conserved on recombinant MPO. We found that human MPO autoantibody response was not restricted to a single epitope on native MPO, as all sera tested did not show the same profile in competitive studies with monoclonals. Furthermure, 30% of human anti-native MPO sera failed to recognize rMPO

Light induced relaxation dynamics of the ferricyanide ion revisited by ultrafast XUV photoelectron spectroscopy

The photoexcited ferricyanide undergoes an ultrafast spin crossover followed by Jahn–Teller distortion.</p