Plasma Accelerators and Ultrafast X-rays
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 light at nanometre wavelengths with visible driving lasers. We are studying so-called quasi-phase-matching methods, which could increase the efficiency of HHG by orders of magnitude. In the longer term we aim to work with chemists and physicists on experiments to use these novel sources of bright x-radiation.
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 of up to 1 GeV — an energy typical of that used in present generation synchrotrons and free-electron lasers — in an acceleration stage only 30 mm long. We are presently working on techniques to control the injection of particles into the plasma wave, staging of plasma accelerators, and using these laser-accelerated electron beams to generate ultrafast x-ray pulses.