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Professor Simon Hooker

Tutor in Physics, Professor of Atomic & Laser Physics

Subject

Physics

Research

I study the interaction of very high intensity laser pulses with plasma. Several important applications arise from such applications, including the generation of very short X-ray pulses 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 beams with nanometre wavelengths by visible driving lasers. My research group studies methods for increasing the efficiency of these sources, and especially so-called quasi-phase-matching methods. We also investigate the application of HHG beams to imaging objects without the aid of conventional lenses (which are not readily available for X-ray wavelengths). In 'lensless imaging' one instead records the diffraction pattern produced by the object and deduces the spatial distribution of the object by employing numerical algorithms; it turns out that this can be done rather efficiently even though the important phase information is lost when the detector records the intensity (rather than amplitude) of the diffraction pattern.

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. My research group has 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.

Teaching Interests

At Merton I give undergraduate tutorials in Electromagnetism and Optics for the first- and second-year physicists, and Atomic and Molecular Physics for the third-year. Within the Department I give lectures on Laser Physics and on Molecular Physics to second- and third-year physicists.

Photo: courtesy Oxford University Department of Physics