Focusing a high-power femtosecond laser pulse into plasma produces an electrostatic wake which can be harnessed to accelerate electrons to GeV energies in several centimetres. A ponderomotive force (red arrows in the figure) arising from the light pressure pushes aside the plasma electrons to generate the wake. The electrostatic fields associated with this wake is utilised to produce accelerating fields which are 3-4 orders of magnitude larger than is possible in the RF cavity of a conventional accelerator.

The excitation of a plasma wakefield is analogous to the wave behind a motorboat on a lake. If a short bunch of electrons is injected at an appropriate phase into the electrostatic wave, it can be accelerated by the Coulomb force associated with the wakefield (black arrows). In our analogy, a surfer riding the wave behind the motorboat would gain energy from the wave. Ultra-short, ultra-intense laser pulses from commercially available table-top terawatt femtosecond lasers are suitable drivers of plasma wakes. Eventually, using several Joules of laser energy, we expect to produce electron bunches with a mean energy above 1 GeV, an energy spread of about 1% and a peak current exceeding 1 kA . However, to demonstrate the technology, the energy will initially be restricted to ~100 MeV.