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Our group studies applications arising the interaction of very high intensity laser pulses with plasma. These include compact sources of soft x-ray radiation and a new type of particle accelerator known as a plasma accelerator.

In high-harmonic generation (HHG) the highly nonlinear interaction between high-intensity laser pulses and atoms generates odd harmonics of the frequency of the driving laser. Very high-order harmonics are possible — the harmonic order can reach several hundred — allowing the generation of coherent light at nanometre wavelengths with visible driving lasers. We study methods for increasing the generation efficiency as well as applications of high-harmonic beams, such as ultrafast, "lensless" X-ray imaging.

At intensities of around 10²² W m^-2, laser pulses propagating through a plasma generate a longitudinal plasma wave which trails the laser pulse in much the same way a wake follows a boat travelling across water. The electric fields in the plasma wave can reach 100 kilovolts per micron, at least a thousand times bigger than the accelerating fields used in the LHC at CERN. We have used this approach to generate electron beams with energies comparable to those used in large-scale synchrotrons and free-electron lasers — but in an acceleration stage only 30 mm long. We are presently working on new ideas for driving plasma accelerators at very high repetition rates, techniques for controlling the injection of particles into the plasma wave, and using the laser-accelerated electron beams to generate ultrafast x-ray pulses.