Intra-pulse transition between ion acceleration mechanisms in intense laser-foil interactions

Padda, H. and King, M. and Gray, R. J. and Powell, H. W. and Izquierdo, Bruno and Stockhausen, L. C. and Wilson, R. and Carroll, D. C. and Dance, R. J. and MacLellan, D. A. and Yuan, X. H. and Butler, N. M. H. and Capdessus, R. and Borghesi, M. and Neely, D. and McKenna, P. (2016) Intra-pulse transition between ion acceleration mechanisms in intense laser-foil interactions. Physics of Plasmas, 23 (6). ISSN 1070-664X

[img]
Preview
Text (Padda-etal-POP-2016-Intra-pulse-transition-between-ion-acceleration-mechanisms)
Padda_etal_POP_2016_Intra_pulse_transition_between_ion_acceleration_mechanisms.pdf
Accepted Author Manuscript

Download (6MB)| Preview

    Abstract

    Multiple ion acceleration mechanisms can occur when an ultrathin foil is irradiated with an intense laser pulse, with the dominant mechanism changing over the course of the interaction. Measurement of the spatial-intensity distribution of the beam of energetic protons is used to investigate the transition from radiation pressure acceleration to transparency-driven processes. It is shown numerically that radiation pressure drives an increased expansion of the target ions within the spatial extent of the laser focal spot, which induces a radial deflection of relatively low energy sheath-accelerated protons to form an annular distribution. Through variation of the target foil thickness, the opening angle of the ring is shown to be correlated to the point in time transparency occurs during the interaction and is maximized when it occurs at the peak of the laser intensity profile. Corresponding experimental measurements of the ring size variation with target thickness exhibit the same trends and provide insight into the intra-pulse laser-plasma evolution.