Classical trajectories in polar-asymmetric laser fields: Synchronous THz and XUV emission

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Synchronous extreme ultraviolet (XUV) and single-cycle terahertz (THz) bursts are generated in argon plasma induced by intense two-color femtosecond laser pulses. Correlations between the intensity of the even and odd high-harmonics and the THz radiation are found by studying the phase-delay between the excitation pulses at 800 and 400 nm as well as the degree of polar asymmetry in the incident electric field. Experiments in both the weak- and strong- polar asymmetric regimes show remarkable agreement with a simple analytical model based on classical electron trajectories in an arbitrary synthetic electric field.