Dynamics of energy deposition of highly relativistic laser pulses in aligned nanowire arrays*

The ultrahigh energy density matter regime can be reached by irradiating arrays of vertically aligned nanowires with ultrahigh contrast fs laser pulses of relativistic intensities and joule-level energy [Ref 1,2]. The laser pulses penetrate deep into the array volumetrically heating the near solid density nanowire targets to multi-keV temperatures. As the wires explode a super-critical plasma fills the inter-wire gaps preventing further optical light from efficiently coupling into the volumetric plasma. Here we present the first results of the energy deposition dynamics into aligned Ni nanowires arrays at intensities up to 2 x 10²¹ Wcm^-2 based on monitoring the x-ray emission and He-like ions line intensities. At these highly relativistic intensities the gaps in arrays of 100 nm diameter wires with average density 7% or 24 % solid density are measured to remain open for >100 fs. Knowledge of the gap closure dynamics will allow for optimal design of nanowire targets to match the pulse width and intensity of a given laser driver.

1. M.A. Purvis, et al, Nature Photonics 7, 796 (2013).
2. B. Bargsten, et al, Science Advances, 3,e1601558(2017).