Harmonics generation in electron-ion collisions in a short laser pulse
  Anomalously high generation efficiency of coherent higher field-harmonics in collisions between {\em oppositely charged particles} in the field of femtosecond lasers is predicted. This is based on rigorous numerical solutions of a quantum kinetic equation for dense laser plasmas which overcomes limitations of previous investigations. 
H. Haberland, M. Bonitz, and D. Kremp