A new RIXS analyzer scheme based on transmission zone plates

Resonant inelastic X-ray scattering (RIXS) is a rapidly developing X-ray spectroscopy technique with the capability to study elementary excitations of electrons, phonons and spins. To date, RIXS instrumentation in the XUV and the soft X-ray range heavily relied on reflecting variable line spacing (VLS) analyzer gratings that collect the emitted light and disperse it across a detector. Such VLS gratings do not provide imaging capabilities, meaning that no information from the sample is conveyed along the non-dispersive direction of the detector.

In order to overcome this drawback, the X-Ray Optics and Applications Group at the Laboratory for Micro-and Nanotechnology of PSI has successfully implemented a new spectral analyzer scheme based on off-axis transmission Fresnel zone plates. The advantage of this new approach is that such optics feature imaging capabilities, which were verified in an initial experiment at the SLS-ADRESS beam line [1]. In a collaboration with scientists from Göttingen (MPI for Biophysical Chemistry and Institute for X-Ray Physics) and Hamburg (DESY), the novel detection scheme was successfully implemented at the P04 beamline of PETRA III at DESY. By varying the photon energy along a line focus on the sample, it was possible to simultaneously record the emission spectra of a jet of liquid acetonitrile over a range of excitation energies, providing a map of RIXS spectra in a single experiment. Moreover, by scanning a line focus across the sample in one dimension, spectrally resolved RIXS 2D images were recorded for the first time [2]. This new scheme of analyzer optics leads to an increase of the throughput of measurements by several orders of magnitude compared to conventional approaches. Additionally, it opens up a variety of novel measurement classes at synchrotrons and efficient, ultra-fast time resolved investigations at X-ray Free-Electron Laser sources.