X-ray Generation From Ultra-High Energy Density Relativistic Plasmas by Ultrafast Laser Irradiation of Nanowire Arrays

Abstract

We have demonstrated the volumetric heating of near-solid density plasmas to keV temperatures using ultra-high contrast femtosecond laser pulses of only 0.5 J energy to irradiate arrays of vertically aligned nanowires (Purvis et al. Nat Photonics 7:796–780, 2013). Our x-ray spectra and particle-in-cell (PIC) simulations show extremely highly ionized plasma volumes several micrometers in depth are generated by irradiation of Au and Ni nanowire arrays with femtosecond laser pulses of relativistic intensities. Arrays of vertically aligned Ni nanowires with an average density of 12 % solid were ionized to the He-like stage. The He-like line emission from the nanowire target exceeds the intensity of the Ni Kα line at this irradiation intensity. Similarly near-solid density Au nanowire arrays were ionized to the Co-like (Au52+). This volumetric plasma heating approach creates a new laboratory plasma regime in which extreme plasma parameters can be accessed with table-top lasers. Scaling to higher laser intensities promises to create plasmas with temperatures and pressures similar to those in the center of the sun. The increased hydrodynamic-to-radiative lifetime ratio is responsible for a dramatic increase in the x-ray emission with respect to polished solid targets. As highly efficient X-ray emitters and sources of extreme plasma conditions, these plasmas could play a role in the development of new ultra-short pulse soft x-ray lasers.