Multi-chromatic narrow-energy-spread electron bunches from laser   wakefield acceleration with dual-color lasers
  A method based on laser wakefield acceleration with controlled ionization injection triggered by another frequency-tripled laser is proposed, which can produce electron bunches with low energy spread. As two color pulses co-propagate in the background plasma, the peak amplitude of the combined laser field is modulated in time and space during the laser propagation due to the plasma dispersion. Ionization injection occurs when the peak amplitude exceeds certain threshold. The threshold is exceeded for limited duration periodically at different propagation distances, leading to multiple ionization injections and separated electron bunches. The method is demonstrated through multi-dimensional particle-in-cell simulations. Such electron bunches may be used to generate multi-chromatic X-ray sources for a variety of applications. 
Ming Zeng, Min Chen, Lu-Le Yu, Warren B. Mori, Zheng-Ming Sheng,   Bernhard Hidding, Dino Jaroszynski, Jie Zhang
physics.plasm-ph