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Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P67
Quantitative gas-phase experiments with femtosecond soft X-ray free-electron
laser pulses at FLASH
Mathias Richter 1 , Andrei Sorokin 1,2 , Sergey Bobashev 2 , Kai Tiedtke 3
1 Physikalisch-Technische Bundesanstalt, Abbestr. 2-12, 10587 Berlin, Germany – 2 Ioffe
Physico-Technical Institute, Polytekhnicheskaya 26, 194021 St. Petersburg, Russia –
3 Deutsche Elektronen-Synchrotron, Notkestr. 85, 22603 Hamburg, Germany
Recent progress in the development of powerful vacuum-ultraviolet radiation and soft
X-ray (XUV) sources such as higher harmonics generation sources and free-electron
lasers (FELs) has allowed to extend the study of ultra-fast and non-linear effects on
the interaction of highly intense electromagnetic radiation with matter considerably
from the optical regime to the spectral range above atomic ionization thresholds. In
this context, we present first results of pulse resolved gas-phase experiments obtained
at the new XUV-FEL facility FLASH in Hamburg. Emphasis was laid on the determination
of absolute photon numbers per pulse with the help of a calibrated setup [1]
which allows the investigation of non-linear effects by quantitative measurements. In
our contribution, we will discuss the competition between direct and sequential multiphoton
ionization, e.g. in molecular nitrogen [2], and the influence of Coulomb explosion
and space charge on ion time-of-flight spectra (see, e.g., Fig. 1). Moreover, a new
method for the determination of spot size and beam waist on focused XUV-FEL beams
will be presented which is based on a saturation effect upon atomic photoionization [3].
[1] M. Richter et al., Appl. Phys. Lett. 83 (2003) 2970.
[2] A.A. Sorokin et al., submitted to J. Phys. B.
[3] A.A. Sorokin et al., submitted to Appl. Phys. Lett.
Fig. 1: Two single-shot
ion time-of-flight spectra of
neon obtained from two subsequent
FEL pulses, respectively,
with 750 (red) and
150,000 (blue) ions generated
within the first pulse.