Increased X-ray Yield from Femtosecond Laser Irradiation of Vertically Aligned Nanostructures

Our purpose is to demonstrate a novel approach for converting optical laser energy pulses into bright picosecond x-ray pulses at a high conversion efficiency. In order to do this, a high contrast, femtosecond Ti:saph laser is used to irradiate vertically aligned nanostructure targets. This allows for the volumetric heating of the nanowire structure, creating multi-KeV temperature, near solid density plasmas with increased X-ray yields due to the greatly decreased cooling lifetime to hydrodynamic lifetime ratio-- a key component in conversion efficiency. Using a set of 12 filtered Si diodes and a bent Mica crystal spectrometer, we monitored the x-ray yield and spectra in different regions on a shot by shot basis. We have measured a conversion efficiency of 5{\%} for hv\textgreater 900eV in 2 pi radians for Au wires irradiated with pulses of 5x10\textasciicircum 18Wcm\textasciicircum -2.~