The SQS (Small Quantum Systems) instrument is dedicated to investigations of fundamental processes of light-matter interaction in the soft X-ray wavelength regime. Typical targets are isolated species in the gas phase, such as atoms, molecules, ions, clusters, nanoparticles and large bio-molecules. The main applications focus on processes occurring under irradiation with ultra-short, highly intense X-ray pulses using a variety of spectroscopic techniques.  In particular, studies of non-linear phenomena, such as multiple ionization and multi-photon processes, time-resolved experiments following dynamical processes on the femtosecond timescale, and investigations using coherent scattering techniques are targeted.

The experiments will be performed using a state-of-the art experimental platform taking advantage of the ultrashort pulses, the extreme brilliance and the high coherence of the SASE3 undulator at the European XFEL that will be combined with a powerful and tunable optical laser system. The SQS instrument will provide three experimental stations to the scientific community:

AQS (Atomic-like Quantum Systems) dedicated principally to experiments on atoms and small molecules,

NQS (Nano-size Quantum Systems) dedicated principally to investigation on larger systems, such as clusters and nano-particles,

SQS-REMI (REaction MIcroscope) enabling the complete characterization of the ionization and fragmentation process, at least for smaller systems, by analyzing all products created in the interaction of the target with the FEL pulses.

A wide range of experimental techniques for spectroscopic investigations using electrons, ions and photons will be available and various set-ups for introducing the target sample. The design of the spectrometers has been optimized to take advantage of the high repetition rate and to enable various types of coincidence methods. The use of soft X-ray photons enables controlled excitations of specific electronic subshells in atomic and site- or element specific excitation in molecular targets.