Characterization of High-Intensity Laser Propagation in the Relativistic Transparent Regime through Measurements of Energetic Proton Beams

Willingale, L. and Nagel, S. R. and Thomas, A. G. R. and Bellei, C. and Clarke, R. J. and Dangor, A. E. and Heathcote, R. and Kaluza, M. C. and Kamperidis, C. and Kneip, S. and Krushelnick, K. and Lopes, N. and Mangles, S. P. D. and Nazarov, W. and Nilson, P. M. and Najmudin, Z. (2009) Characterization of High-Intensity Laser Propagation in the Relativistic Transparent Regime through Measurements of Energetic Proton Beams. Physical review letters, 102 (12): 125002. ISSN 0031-9007

Abstract

Experiments were performed to investigate the propagation of a high intensity (I similar to 10(21) W cm(-2)) laser in foam targets with densities ranging from 0.9n(c) to 30n(c). Proton acceleration was used to diagnose the interaction. An improvement in proton beam energy and efficiency is observed for the lowest density foam (n(e)=0.9n(c)), compared to higher density foams. Simulations show that the laser beam penetrates deeper into the target due to its relativistic propagation and results in greater collimation of the ensuing hot electrons. This results in the rear surface accelerating electric field being larger, increasing the efficiency of the acceleration. Enhanced collimation of the ions is seen to be due to the self-generated azimuthal magnetic and electric fields at the rear of the target.