1-Andre D Bandrauk.pmd

Interaction of intense ultrashort (few-cycle) laser pulses with atoms and molecules leads to a highly nonlinear nonperturbative regime of electron dynamics and response. Ionized electrons are shown to be controlled by such pulses and the response is described by simple classical models of under and above barrier ionization followed by recollision with the parent ion or collision with neighboring ions in molecules. Harmonic generation in such a nonperturbative regime produces photons with maximum energy predicted by simple classical models of collisionrecollision for both linearly and circularly polarized pulses. This highly nonlinear generation of high energy photons is currently the main source of attosecond pulses.