Instrumental development of X-ray atomic holography at ESRF

We have developed an X-ray Fluorescence Holography (XFH) setup at the European Synchrotron Radiation Facility (ESRF). The main difficulty inherent to XFH is that the holographic signal is in the low 10−3 range compared to the background isotropic fluorescent radiation. This requires a very pure fluorescent signal and the highest possible count rate. Therefore, we designed a focusing analyser system with large solid angle acceptance. The photons of the focused beam were counted by an avalanche photodiode in single-photon counting mode up to a few MHz. At even higher intensity, we switched to a Si diode working in the photocurrent mode. Due to the relatively weak requirements on the bandwidth of the exciting incident radiation, we could directly use the undulator beam, discriminating lower harmonics by an absorber and higher ones by reflecting the beam on a Si mirror. By developing a fast, continuous “spiral” scanning technique, a full hologram could be recorded in 30 sec.