Recollisions and high-harmonic generation

We describe the Recollision Model of high-harmonic generation, in which electrons escape from atomic Coulomb binding in intense laser fields by tunneling, are ponderomotively accelerated, and recollide on return to the parent ionic core. High harmonics are generated by Bremsstrahlung, modulated by the coherent periodic nature of the tunneling process. Harmonic plateaux involve the time-dependent dipole induced by the returning wave packets. We show how atomic wave packets are generated and manipulated by strong laser driving fields, and link the recollision to nonsequential ionization.