Beamline FL 26

Picture of the REMI instrument installed at FL26 in the FLASH2 experimental hall ‘Kai Siegbahn’.

Sketch of the major components of the REMI: The ion (blue) and electron (red) time-of-flight spectrometers with various electrodes and Helmholtz coils to establish electric and magnetic extraction fields, respectively. A target source is shown producing a vertical gas beam (white). Different types of target sources have been used with the REMI so far, such as effusive and supersonic gas beams as well as a liquid water jet. A split back-reflecting refocusing mirror allows for time-dependent investigations in the fs-regime. A different in-line delay and focusing scheme will be installed in the near future avoiding the photon beam passing the interaction region twice. Because of the open spectrometer design the vacuum requirements are very demanding in order to suppress the background signal.

With a reaction microscope (REMI) all fragments of a photoionization process can be detected by means of a combination of electron and ion time-of-flight spectrometers and a specific arrangement of electric and magnetic extraction fields [1]. Using a coincident measurement technique, a complete set of all the kinematic properties of the products of the photoionization process can be determined in the experiment. Hence, this device is especially suited to investigate the dynamics of various ionization processes of gas phase and liquid targets.

Over the past years, a number of remarkable scientific results derived from REMI-experiments at FLASH1 have been published by the group of R. Moshammer (MPIK), e.g. regarding the dynamics of inter-molecular coulombic decay processes in weakly-bound rare gas dimers [2] and the dynamics in the dissociation of multiply-charged iodine molecules [3]. With a similar apparatus, the COLTRIMS instrument of the group of R. Dörner of UNI Frankfurt, the existence of so-called Efimov-states in the helium trimer could be proven and very precise measurements of structure and the extremely low binding energies of the He-trimer as well as the He-dimer were successful [4,5].

As a user experimental set-up temporarily installed for a specific beamtime, the complexity of the REMI instrument and especially the demanding vacuum requirements result in long preparation phase before the actual experiment.

Hence, in collaboration with the group of R. Moshammer of MPIK Heidelberg a REMI apparatus has been set-up as a permanent endstation at a dedicated beamline of FLASH2 in order to improve the efficiency of the scientific work with such a powerful as well as complex instrument. In the near future, it is planned to make this endstation available to all user groups interested in atomic and molecular science.

[1] J. Ullrich et al., Recoil-ion and electron momentum spectroscopy: reaction-microscopes, Rep. Prog. Phys. 66, pp. 1463–1545, (2003)
[2] K. Schnorr et al., Time-Resolved Measurement of Interatomic Coulombic Decay in Ne2 , Phys. Rev. Lett. 111, 093402 (2013)
[3] K. Schnorr et al., Electron Rearrangement Dynamics in Dissociating I2n+ Molecules Accessed by Extreme Ultraviolet Pump-Probe Experiments, Phys. Rev. Lett. 113, 073001 (2014)
[4] S. Zeller et al., Imaging the He2 quantum halo state using a free electron laser, arXiv_1601.03247v1 (2016)
[5] M. Kunitski et al., Observation of the Efimov state of the helium trimer, Science 348, p. 551-555 (2015)

CONTACT FL 26 Beamline:
Markus Braune
E-Mail: Markus Braune
Phone: +49 (0)40 8998 (9)1730
Location: 28k / O2.021