Influence of spatial-intensity contrast in ultraintense laser-plasma interactions

Wilson, R. and King, M. and Butler, N. M. H. and Carroll, D. C. and Frazer, T. P. and Duff, M. J. and Higginson, A. and Dance, R. J. and Jarrett, J. and Davidson, Z. E. and Armstrong, C. D. and Liu, H. and Hawkes, S. J. and Clarke, R. J. and Neely, D. and Gray, R. J. and McKenna, P. (2022) Influence of spatial-intensity contrast in ultraintense laser-plasma interactions. Scientific Reports, 12. 1910. ISSN 2045-2322 (

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Increasing the intensity to which high power laser pulses are focused has opened up new research possibilities, including promising new approaches to particle acceleration and phenomena such as high field quantum electrodynamics. Whilst the intensity achievable with a laser pulse of a given power can be increased via tighter focusing, the focal spot profile also plays an important role in the interaction physics. Here we show that the spatial-intensity distribution, and specifically the ratio of the intensity in the peak of the laser focal spot to the halo surrounding it, is important in the interaction of ultraintense laser pulses with solid targets. By comparing proton acceleration measurements from foil targets irradiated with by a near-diffraction-limited wavelength scale focal spot and larger F-number focusing, we find that this spatial-intensity contrast parameter strongly influences laser energy coupling to fast electrons. We find that for multi-petawatt pulses, spatial-intensity contrast is potentially as important as temporal-intensity contrast.