Two teams now report rapid acceleration of electrons using small silica structures to shape light fields into patterns similar to those in a linear accelerator. In both of the experiments, the researchers sent electrons skating just over a silica surface that contained narrow grooves in the direction perpendicular to the electron beam. They then shined ultrashort laser pulses directly onto the surface (called a grating), which generated a pattern where the electric field was alternately enhanced and diminished in neighboring “zones” just above the surface. This pattern of fields reversed direction twice during every oscillation cycle of the laser light and could accelerate electrons (see YouTube video).
Here's the YouTube video:
Of course, with any initial advancement, there's still plenty of work to do. For many applications, getting to higher energy alone isn't the only issue. In FEL's, for example, the emittance of the beam is equally crucial. So accelerating scheme such as this must show the ability to not cause an emittance blow-up. The other issue that is often critical is the question on how much charge per bunch that can be accelerated. For many applications, the standard "high-brightness" beam requires a 1 nC per bunch charge. So the scheme must be able to handle beams of that magnitude without sacrificing the quality.
Still, this promises to be another exciting avenue for future accelerators.