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LXD Spectroscopy: Laser Pump/ X-ray Probe Spectroscopy

In order to study ultrafast dynamical processes in liquid biochemical system under real conditions our group is establishing a Laser-pump/ soft X-ray-probe setup at BESSYII. Therefore the sample is excited by a short pulsed Laser, and is probed afterwards by means of XAS.

This method has been applied successfully in the hard X-ray regime for investigations elements in biochemical systems, e.g. the iron atom in the active center of hem-proteins. In the hard X-ray regime the K-edge is probed at an energy of 7100eV.

By extending the method to the soft X-ray regime (200eV-2000eV) the investigation of lightweight atoms (C, O, N…etc), which are essential for biological processes, becomes possible. Additionally, XAS measurements in the soft X-ray regime reveal detailed information about the chemical binding, and thus the interaction of the system with the environment. Soft X-ray L-edge spectroscopy for transition metals is more appropriate as L-edge features deliver direct information about the d-orbital, which is involved in the binding of ligands to the iron atom in hem-proteins.

The biggest challenge of this method, besides the precise spatiotemporal matching of the Laser and the X-ray, is the detection of extremely weak fluorescence signals. Furthermore, the investigation of flowing samples (using a flow cell or a liquid jet) prevents radiation-induced sample damage.

Further application for this method would be to extent it to the XFEL and gain from its faster time resolution (femto second regime) and the higher photon flux.