  Strong optical laser fields modify the way x rays interact with matter. This
allows us to use x rays to gain deeper insight into strong-field processes.
Alternatively, optical lasers 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. Topics addressed include the impact of spin-orbit interaction on
the alignment of atomic ions produced in a strong laser field,
electromagnetically induced transparency in the x-ray regime, and laser-induced
alignment of molecules.
