Strong-Field Control of X-Ray Processes

In x-ray science, cross-sections for x-ray absorption in matter are typically assumed to be invariants, depending only on the atomic and spatial composition of the material. However, by utilizing strong electromagnetic fields, it is possible to modify x-ray absorption cross-sections in a controlled way. This allows one to use x-rays to gain deeper insight into strong-field processes. As an application, strong electromagnetic fields may be utilized to control the propagation of x-rays through a medium. Gas-phase systems are particularly suitable for illustrating the basic principles underlying combined x-ray and laser interactions. We discuss three different scenarios for modifying resonant x-ray absorption near an inner-shell edge: (1) Strong-field ionization of the target particles at laser intensities in the range 10(14)-10(15) W/cm(2); (2) modification of electronic structure of inner-shell-excited systems by laser dressing at 10(12)-10(13) W/cm(2); (3) control of resonant x-ray absorption by molecules through laser-induced spatial alignment at 10(11)-10(12) W/cm(2).