Laser-induced k -alignment echoes and 4πphase-space analysis

We report on the experimental and theoretical investigation of alignment echoes of N2O molecules induced by a pair of time-delayed femtosecond laser pulses with different polarizations. When circularly polarized kick pulses are applied, the alignment echoes in the laser propagation direction are activated, giving rise to k-alignment echoes. In these cases, the conventional 2πphase-space analysis, where molecules are restricted to rotate in the plane perpendicular to the laser propagation direction, cannot capture the complete echo information. Thus, we consider the rotational dynamics of molecules in the three-dimensional space and adopt a full phase-space analysis involving evolution in both azimuthal and polar directions, termed 4πphase-space analysis, to reveal the underlying physical mechanism of k-alignment echoes. Its mechanism results from a joint contribution of the filamentation in both azimuthal and polar phase spaces. Our classical and quantum simulations are consistent with the experimental observations.