Au L shell emission from nanowire arrays irradiated at highly relativistic intensities*

Irradiating ordered nanostructure arrays with high contrast, femtosecond laser pulses at relativistic intensities allows for a unique combination of nearly complete optical absorption and light penetration much deeper than the typical optical penetration depth. This results in the volumetric heating of near solid density plasmas to multi keV temperatures up to several micron in depth [1]. Here we present the first results of Au nanowires volumetrically heated with highly relativistic femtosecond pulses with intensities up to 4x10²¹ Wcm^-2. Time integrated x-ray spectra show strong line emission from the L shell of Au with sufficient resolution to identify different charge states up to Ne-like Au (Au⁺⁶⁹).  The increased volume of this plasma hampers the hydrodynamic expansion time while the large electron density contributes to a faster radiative cooling time, creating a more efficient x-ray source than solid density targets [2]. Experimental results will be presented and compared to the result of detailed particle in cell simulations.

1. M.A. Purvis et al Nature Photonics 7, 796 (2013)
2. R. Hollinger et al Optica 4, 1344-1349 (2017)