A hard X-ray pulse source driven by short pulse laser

Electrons accelerated by the interaction between an ultrashort laser pulse and a plasma and then injected into a cold target can create X-ray photons via bremsstrahlung as well as inner shell ionization. The burst of K X-ray fluorescence from a metallic target is typically up to 10¹² photons/pulse with a duration of 100∼600 fs. Dr. F. Zamponi (Friedrich-Schiller-University Jena, Germany) and his colleagues have recently published an interesting report. Thin titanium foils were irradiated by ultraintense laser pulses at intensities up to ≈5×10¹⁹ W/cm², and X-rays emitted from the front and rear sides were measured using a high-resolution imaging system, which allows spectral analysis. During the experiments, they found significant differences in intensity, dimension, and spectrum between front and rear side X-ray emission in the 3~12 keV range. They explained such differences in terms of directional bremsstrahlung emission from fast electrons generated during the interaction process. For more information, see the paper, "Directional Bremsstrahlung from a Ti Laser-Produced X-Ray Source at Relativistic Intensities in the 3-12 keV Range", F. Zampon et al., Phys. Rev. Lett., 105, 085001 (2010).