Spatially and Spectrally Resolved X-ray Fluorescence From a Nitrogen Plasma Channel*

We performed a demonstration experiment using x-ray emission spectroscopy to directly observe the spatial and temporal evolution of excited state populations in photoexcited molecular nitrogen. A novel one dimensional imaging spectrometer in the small quantum systems instrument at the European XFEL spatially and spectrally resolved soft x-ray-induced emission in a dense gas of molecular nitrogen along the x-ray propagation direction. We observed long-lived x-ray induced dynamics by varying the repetition rate of the XFEL to effectively perform an x-ray/x-ray pump/probe experiment. We also used an NIR ultrafast laser to optically excite the nitrogen and the x-ray emission probe to observe population redistribution. The results of this experiment demonstrate high spatial and spectral resolution of this new spectrometer and provides a proof of concept for future laser-based experiments.