Single-shot characterisation of independent femtosecond extreme ultraviolet free electron andf infrared laser pulses

Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses of the femtosecond extreme ultraviolet (XUV) free electron laser in Hamburg and an independent intense 120 fs mode-locked Ti:sapphire laser. Characteristic sidebands appear in the photoelectron spectra when the two pulses overlap spatially and temporally. The cross-correlation curve points to a 250 fs rms jitter between the two sources at the experiment. A more precise determination of the temporal fluctuation between the XUV and infrared pulses is obtained through the analysis of the single-shot sideband intensities. ©2007 American Institute of Physics

An experiment for two-color photoionization using high intensity extreme-UNT free electron and near-IR laser pulses

We describe an experimental system designed for single-shot photoelectron spectroscopy on free atoms and molecules at the Free Electron Laser in Hamburg (FLASH at DESY). The combination of the extreme ultra-violet (EUV) Free Electron Laser and a temporally synchronized optical fs laser (Ti:Sapphire) enables a variety of two-color pump-probe experiments. The spectral, temporal and spatial characteristics of both the EUV FEL and the optical laser pulses, the experimental procedure to control their overlap as well as the performance of an electron spectrometer used to obtain single-shot photoelectron spectra are discussed. As an illustration of the capabilities of this set-up, some results on two-photon two-color ionization of rare gases are presented. (c) 2007 Elsevier B.V. All rights reserved.

Soft x-ray free electron laser microfocus for exploring matter under extreme conditions

We have focused a beam (BL3) of FLASH (Free-electron LASer in Hamburg: lambda = 13.5 nm, pulse length 15 fs, pulse energy 10-40 mu J, 5Hz) using a fine polished off-axis parabola having a focal length of 270 mm and coated with a Mo/Si multilayer with an initial reflectivity of 67% at 13.5 nm. The OAP was mounted and aligned with a picomotor controlled six-axis gimbal. Beam imprints on poly(methyl methacrylate) -PMMA were used to measure focus and the focused beam was used to create isochoric heating of various slab targets. Results show the focal spot has a diameter of

Modelling the cycling of persistent organic pollutants (POPs) in the North Sea system: Fluxes, loading, seasonality, trends

The fate and cycling of two selected POPs is investigated for the North Sea system with an improved version of a fate and transport ocean model (FANTOM). The model uses atmospheric data from the EMEP MSC East POP model (Gusev et al., 2009), giving reasonable concentrations and seasonal distributions for the entire region, as opposed to the three observation stations that Ilyina et al. (2006) were limited to. Other model improvements include changes in the calculation of POP exchange between the water column and sediment.

We chose to simulate the fate of two POPs with very different properties, ?-HCH and PCB 153. Since the fate and cycling of POPs are strongly affected by hydrodynamic processes, a high resolution version of the Hamburg Shelf Ocean Model (HAMSOM) was developed and utilised. Simulations were made for the period 1996–2005. Both models were validated by comparing results with available data, which showed that the simulations were of very satisfactory quality.

Model results show that the North Sea is a net sink for ?-HCH and a net source to the atmosphere of PCB 153. Total masses of ?-HCH and PCB 153 in 2005 are reduced to 30% and 50%, respectively, of 1996 values.

Storms resuspending bottom sediments into the water column mobilise POPs into the atmosphere and have the potential to deliver substantial loads of these POPs into Europe.