High flux coherent supercontinuum soft X-ray source driven by a   single-stage 10 mJ, kHz, Ti:sapphire laser amplifier
  We demonstrate the highest flux tabletop source of coherent soft X-rays to date, driven by a single-stage 10 mJ Ti:sapphire regenerative amplifier at 1 kHz. We first down-convert the laser to 1.3 um using a parametric amplifier, before up-converting it to soft X-rays using high harmonic generation in a high-pressure, phase matched, hollow waveguide geometry. The resulting optimally phase matched broadband spectrum extends to 200 eV, with a soft X-ray photon flux of > 10^6 photons/pulse/1% bandwidth at 1 kHz, corresponding to > 10^9 photons/s/1% bandwidth, or approximately a three order-of-magnitude increase compared with past work. Finally, using this broad bandwidth X-ray source, we demonstrate X-ray absorption spectroscopy of multiple elements and transitions in molecules in a single spectrum, with a spectral resolution of 0.25 eV, and with the ability to resolve the near edge fine structure. 
Chengyuan Ding, Wei Xiong, Tingting Fan, Daniel D. Hickstein, Tenio   Popmintchev, Xiaoshi Zhang, Mike Walls, Margaret M. Mu...
physics.optics