Speaker
Robbie Wilson
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.204.pdf
Enhanced laser-energy absorption in laser-foil interactions driven by
recirculating electron currents
R. Wilson1, R. J. Gray1, M. King1, S. D. R. Williamson1, R. J. Dance1, C. Armstrong1,2, C.
Brabetz3, F. Wagner3, B. Zielbauer3, V. Bagnoud3, D. Neely2,1, P. McKenna1
1
SUPA Department of Physics, University of Strathclyde. Glasgow, UK
2
Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire, UK
3
Plasma Physics Department, GSI GSI Helmholtzzentrum fuer Schwerionenforschung
GmbH, D-64291 Darmstadt, Germany
Laser energy absorption in dense plasma is fundamental to a range of intense laser-driven
particle and radiation generation mechanisms. The coupling of energy to plasma electrons
defines the properties of the radiation beams produced and strongly influences the optical
properties of the plasma. Using the high power PHELIX laser at the GSI laboratory, we
measure the total reflected and scattered laser energy as a function of intensity, by using an
integrating (Ulbricht) sphere. We distinguish between the influence of pulse energy and focal
spot size on total energy absorption, in the interaction of intense laser pulses with thin foils.
We confirm the scaling of absorption with intensity by variation of laser pulse energy as
previously reported in reference [1], but find a slower scaling when changing the focal spot
size. The results were recently published in reference [2]. Using 2D particle-in-cell
simulations, we show that the measured differences arise due to energetic electrons
recirculating within the target. These electrons undergo multiple interactions with the laser
pulse, enhancing absorption in the case of a large focal spot. This effect is found to be
dependent on the laser pulse duration, the target thickness and the divergence of the fast
electron beam. The parameter space over which this occurs is explored via an analytical
model. The experimental, simulation and model results will be presented, and the impact of
the results on our understanding of the fundamental physics of laser energy absorption in
solids will be discussed.
[1] Y. Ping et al, Phys. Rev. Lett., 100, 085004 (2008).
[2] R. J. Gray et al, New J. Phys., At press (2018): DOI:10.1088/1367-2630/aab089
