Generation of attosecond unidirectional half-cycle pulses:: Inclusion of propagation effects

Unidirectional half-cycle pulses (HCP) are ideally suitable for shaping, driving, and probing atomic wave packets in momentum space. The shortest HCP presently available have a width of about 500 fs restricting the manipulation of electronic wave packets to those in high-lying Rydberg states. The nonlinear harmonic response of atoms to strong two-color infrared laser pulses with frequencies omega and 2 omega opens up the opportunity to form trains of ultrafast HCP's on an attosecond time scale. In the present contribution, we investigate the influence of macroscopic propagation effects onto the production of HCP and show that trains of unidirectional attosecond HCP's could be produced under experimentally realistic conditions.