Generation of electromagnetic pulses from plasma channels induced by   femtosecond light strings
  We present a model that elucidates the physics underlying the generation of an electromagnetic pulse from a femtosecond laser induced plasma channel. The radiation pressure force from the laser pulse spatially separates the ionized electrons from the heavier ions and the induced dipole moment subsequently oscillates at the plasma frequency and radiates an electromagnetic pulse. 
Chung-Chieh Cheng, E. M. Wright, and J. V. Moloney