Efficient X-ray generation from volumetrically heated aligned nanowire arrays

The trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into an ultra-hot, near-solid density plasma in which the increased hydrodynamic-to-radiative lifetime ratio results in very efficient X-ray generation. Using high contrast (\textgreater~1x10$^{11})$ pulses of 60fs FWHM duration from a frequency doubled ($\lambda =$ 400 nm) high power Ti:Sa laser, arrays of 55nm and 80nm targets with 12{\%} of solid density were irradiated with pulses of 5x10$^{18}$ Wcm$^{-2}$. The Ni nanowire target produced strong He-like line emission that surpasses the K$\alpha $ emission. Conversion efficiency of \textgreater~5{\%} into photons with energy \textgreater~0.9 KeV in a hemisphere was measured. The Au nanowire spectrum displays strong Au M-shell emission with unresolved 4-3 lines from ions ranging from Co-like (Au$^{+52})$ to Ga-like Au (Au$^{+48})$. Filtered photodiode measurements show a $\sim$ 100X emission increase respect to smooth solid targets for photon energies \textgreater~9 keV.