High energy conversion efficiency in laser-proton acceleration by controlling laser-energy deposition onto thin foil targets

Brenner, Ceri Mae and Robinson, A. P. L. and Markey, K. and Scott, R. H. H. and Gray, Ross and Rosinski, M. and Deppert, K. and Badziak, J and Batani, D. and Davies, J.R. and Lancaster, K.L. and Musgrave, I. O. and Norreys, P.A. and Pasley, J. and Roth, M. and Schlenvoight, H-P and Spindloe, C. and Tatarakis, M. and Winstone, T. B. and McKenna, Paul and Neely, David (2014) High energy conversion efficiency in laser-proton acceleration by controlling laser-energy deposition onto thin foil targets. Applied Physics Letters, 104 (8). 081123. ISSN 0003-6951 (https://doi.org/10.1063/1.4865812)

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Abstract

An all-optical approach to laser-proton acceleration enhancement is investigated using the simplest of target designs to demonstrate application-relevant levels of energy conversion efficiency between laser and protons. Controlled deposition of laser energy, in the form of a double-pulse temporal envelope, is investigated in combination with thin foil targets in which recirculation of laser-accelerated electrons can lead to optimal conditions for coupling laser drive energy into the proton beam. This approach is shown to deliver a substantial enhancement in the coupling of laser energy to 5–30 MeV protons, compared to single pulse irradiation, reaching a record high 15% conversion efficiency with a temporal separation of 1 ps between the two pulses and a 5 μm-thick Au foil. A 1D simulation code is used to support and explain the origin of the observation of an optimum pulse separation of ∼1 ps.