How to dress a metal, explained in an article in Nature Communications.

Applying an intense ultrafast light pulses, which provide a time-periodic electronic potential acting together with the lattice ions, defines the forces experienced by electrons in solids, such as metals and semiconductors, Petek and his coworkers have demonstrated that optical field can transiently, on 10^-14 second time scale, modify (dress) the electronic bands in a metal, potentially changing them from an electron to a hole condition  The is important because electron and hole quasiparticles move in the opposite directions in response to an applied electrical field. Petek and his group demonstrate that light can be used to modify electronic band structures of solids as fast as the attosecond (less than 10^-15 second) time scale of oscillation of the optical field of visible light. This could be used for applications ranging from quantum computing to switching of electrical currents a thousand times faster than in any electronic devices in use today.