Attosecond pulses generation with an ellipticity-modulated laser pulse

Attosecond pulse emission using a laser field with time-dependent ellipticity is studied experimentally and theoretically. Our theoretical approach is validated by comparison with experimental VUV spectra. We show in calculations that the VUV emission can be confined into a narrow temporal window in which the fundamental polarization is quasi-linear. We find an analytical equation describing the duration of this window and compare it with numerical results. The requirements for the fundamental field that are necessary to confine this emission to a single attosecond pulse generation are formulated