Laser Wakefield Acceleration (LWFA) of relativistic electron beams, and High Harmonic Generation (HHG) are two of the driving applications of high-power, short-pulse laser interactions with matter.
Quasi-monoenergetic relativistic electron beams can be produced when short laser pulses are focused at intensities exceeding 10^18 W/cm^2 on usually low-Z gas targets. The gas is instantly ionised and a non-linear plasma wave is created. For sufficiently large amplitude plasma waves, the wave breaks, injecting electrons inside the plasma wave where they are accelerated, so far up to energies > 1 GeV within ~ cm. However, high-Z trace elements can be further ionised at close to the peak of the laser pulse, thus releasing more electrons into the plasma wave. These ionisation-injected electrons are accelerated due to the open trapped Hamiltonian curves they lie on. This can significantly reduce the laser requirements for injection and so acceleration can proceed in a more controlled fashion.
HHG occurs when a ~1mJ, ~10 fsec laser is focused on a neutral high-Z gas jet. The bound electrons of the atoms move in response to the ultrafast oscillation of the laser’s electric field. Harmonic photons up to keV energies, are produced through the recollision of the accelerated (but not ionised) electrons with the parent atoms. Novel experiments using multiple gas jets and a combination of different Z gases, has shown an increase in the conversion to high harmonic as well as the control of their coherence.
This research proposal will focus on optimising ionisation induced LWFA production of electron beams, producing high harmonic photon beams from novel gas targets, and finally counter-propagating the two beams, so as to produce a novel, ultra compact, ultrafast, high-energy, hard x-ray coherent source. Such a table-top source has a wide range of applications from the probing of hot-dense matter, and to non-destructive, high resolution, ultrafast biomedical imaging.
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