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By focusing an ultraintense laser onto a helium gaz jet, a collimated beam of ultrafast broadband X-ray radiation can now be generated. The X-ray radiation results from the betatron oscillations of relativistic electrons in the laser created plasma channel. Thus, just as in a synchrotron, the spectral and flux properties of the X-ray beam can be linked to the electron beam through the plasma wiggler strength. The radiation has been observed within 1-10 keV with filters and presents a divergence of as low as 20 mrad. In addition, this source possesses the unique properties to be ultrafast and perfectly synchronized with the laser system, which opens the way toward new types of pump probe experiments.

Exploration of a new ultrafast-ultrasmall frontier in atomic and molecular physics has begun. Not only is it possible to control outer-shell electron dynamics with intense optical lasers, but now control of ultrafast inner-shell processes has become possible by combining strong optical laser fields with tunable sources of X-ray radiation. This marriage of strong-field laser and X-ray physics has led to the discovery of methods to control reversibly resonant X-ray absorption in atoms and molecules on ultrafast timescales. Here we describe three scenarios for control of resonant X-ray absorption: ultrafast field ionization, electromagnetically induced transparency in atoms and strong-field molecular alignment.