Plasma effects in high harmonic spectra from ultrarelativistic laser-plasma interactions

A single particle model has been applied to examine the competition between radiation from a strong Langmuir source and coherent bremsstrahlung in ultra-relativistic laser-plasma interactions. Output from this model shows generally satisfactory agreement with that from particle-in-cell (PIC) simulations, in particular reproducing spectra characterised by a decay index p = 5/3. At the highest intensities considered, both model and PIC spectra show the competing contribution from relativistic electron bremsstrahlung, characterised by a further relaxation in the decay index to p = 2/3. Combinations of laser and plasma parameters have been identified that define regions of parameter space where one or other emission is dominant. (C) 2016 Elsevier B.V. All rights reserved.