Particle Acceleration with High Intensity Mid-IR Lasers.

A well focused high-power (multi-terrwatt) laser pulse is able to deliver intensities on target above 10E19 Wcm^-2 and drive and probe exotic processes on a few femtosecond timescale. Under these extreme conditions, large electric fields, significantly greater than those attainable in a classic RF accelerator structure can be created and exploited. Charged particles such as electrons can be accelerated to relativistic intensities (where mass change becomes significant) over a single optical cycle. It is also possible to create plasma "bubble" structures as an intense light pulse propagates through matter, and this can trap and accelerate electrons to multi-GeV energies over length scales of a few cm.
To date, most laser acceleration experiments have been undertaken using large "National Facility" scale lasers operating at 1um or 800nm. However there are compelling reasons to move to longer wavelength lasers in the so-called Mid-IR spectral range. As the optical cycle time increases for longer wavelengths, electrons experience a greater accelerating force, which scales as wavelength squared. Thus a 4um laser can potentially drive a particle to ~16x higher energies than a 1um laser of equivalent energy and intensity. For a bubble regime accelerator, the situation is further complicated by the need to match a laser pulse to conditions such as dispersion in a plasma, and here longer wavelengths also appear to have some advantages. However there are no high-power (>1TW) commercial MIR laser systems available, and building such a system is a significant technical challenge as there is a lack of "classic" gain storage materials able to operate in this wavelength range with the necessary bandwidth to amplify a sub 100fs pulse.
This project will build on the Chimera multi-wavelength MIR laser being constructed at Imperial College. The student will work to optimise the performance of this complex optical parametric chirped pulse amplification system to enable it to drive and probe high energy density physics experiments. The PhD project will include optimisation of laser pulse compression by measurement and control of high-order phase, and scale up of laser energy to the >100mJ level. The student will model, construct and run and analyse data from laser driven particle acceleration experiments using both the Chimera laser and off site facilities such as the Gemini laser based at the Rutherford Appleton Laboratory.