Study of x-ray emission enhancement via high contrast femtosecond laser   interacting with solid foil
  We studied the hard x-ray emission and the K-alpha x-ray conversion efficiency produced by 60 fs high contrast frequency doubled Ti: sapphire laser pulse focused on Cu foil target. Cu K-alpha photon emission obtained with second harmonic laser pulse is more intense than the case of fundamental laser pulse. The Cu K-alpha conversion efficiency shows strong dependence on laser nonlinearly skewed pulse shape and reaches the maximum value 4x10-4 with 100 fs negatively skewed pulse. It shows the electron spectrum shaping contribute to the increase of conversion efficiency. Particle-in-cell simulations demonstrates that the application of high contrast laser pulses will be an effective method to optimize the x-ray emission, via the Enhanced Vacuum Heating mechanism. 
L. M. Chen, M. Kando, S. V. Bulanov, J. Koga, K. Nakajima, T. Tajima   (Advanced Photon Research Center, Kansai Photon Scien...