Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P71
An autocorrelator and versatile delay line for the VUV FEL at TTF
Marco Rutkowski 1 , Rolf Mitzner 1 , Björn Siemer 1 , Helmut Zacharias 1 ,
Matthias Neeb 2 , Tino Noll 2 , Wolfgang Eberhardt 2
1 Physikalisches Institut, Wilhelm-Klemm Str. 10, 48149 Münster – 2 BESSY GmbH,
Albert EInstein Str. 15, 12489 Berlin
In order to do jitter-free X-ray pump and probe experiments at the VUV FEL (FLASH)
at DESY / Hamburg as well as to characterize the temporal structure of its high power
pulses a novel autocorrelator has been designed for the XUV up to photon energies of
200 eV. The design is based on geometrical beamsplitting of the incomming FEL beam
by a sharp mirror edge into two branches. Due to the limited reflection and the strong
absorption of optical components an all-reflective geometry with grazing incidence
angles at the mirrors has been chosen. The actual design represents a compromize
between size and delay range of the delay line on the one hand and efficiency on the
other hand. Thus it allows the handling of high power pulses and guarantees a high
efficiency (50 %) up to 200 eV. The total delay is about 25 ps with a femtosecond
resolution.
The main challenge arises from the strict requirements regarding the motional resolution
of the mirror movements as well as the mechanical stability of the entire autocorrelator.
To fulfil the requirements on the motional accuracy elastic deformation
(flexure) is used to control the movements. The intrinsic stabilization of the delay
line is achieved by optimizing the stiffness. A further advantage of the autocorrelator
design is the lack of any angle deviation or shift of the beam direction. Thus the autocorrelator
can be integrated permanently into one of the FEL beamlines at the TTF2.
First test experiments at the FEL are planned end of 2006 utilizing two photon photo
emission from noble gases to measure the temporal length of the FEL pulses at 40 eV.