Movie 1. Synthesis of a moving intensity grating. Two laser pulses of different frequencies (blue and red) interfere in a colliding geometry (see text). Both pulses travel with the speed of light. The intensity of the resulting interference pattern (averaged over one temporal optcal cycle) is shown as oscillating pattern (black). Because of the two different optical frequencies, the maxima and minima of such an intensity wave travel with less than the speed of light.

Movie 2. Compression dynamics for attosecond electron pulses. After initiating self-compression by an optical intensity wave, the electron density (blue) begins to accumulate and peaks up to a 15-attosecond duration and then disperses again. The times are given relative to the laser pulse overlap (see text). A different peak time (1.15 ps), as compared to Fig. 5, is the result of a different electron energy in this simulation.