Laser-based femtosecond X-ray pulse source

A Chinese group led by Professor J. Zhang (President of Shanghai Jiao Tong University) recently published a report on the generation of X-ray pulses of around 3 keV by using an Ar clustering gas jet target (~3mm dia.) and a Ti:sapphire laser (power 800 mJ, pulse width 28 fs, wavelength 800 nm, frequency 10 Hz). The intensity of the Ar K-shell emissions in the forward direction was found to be around 10⁴ photons/mrad²/pulse. The group emphasized the significance of laser contrast, which is a ratio of the main pulse and pre-pulse, and found that X-ray flux is reduced by 2 orders of magnitude if the laser pulse contrast decreases from 10⁹ to 10⁷ with constant laser pulse energy. For more information, see the paper, "Intense High-Contrast Femtosecond K-Shell X-Ray Source from Laser-Driven Ar Clusters", L. M. Chen et al., Phys. Rev. Lett. 104, 215004 (2010).