Generation of elliptically polarized high-order harmonics in cross-polarized bichromatic laser pulses: mechanism and control | CU Experts

Abstract; ; We present an analysis based on results of numerical model simulations of microscopic high-order harmonic generation in a cross-polarized laser set-up using the time-dependent Schrödinger equation. The set-up consists of an intense laser pulse at the fundamental frequency corresponding to a wavelength of 800 nm and a weaker second harmonic pulse. In qualitative agreement with the observations in an experiment (Lambert; et al; 2015; Nat. Commun.; 6; 6167) the results of the simulations show that at pulse durations in the regime of 3–8 cycles full-width-at-half-maximum (FWHM) high ellipticities of the even harmonics (scaled in terms of the fundamental frequency) at the cut-off of the spectrum can be achieved. In the long pulse limit (beyond 20 cycles FWHM) those harmonics are close to linearly polarized, consistent with earlier predictions (Shafir; et al; 2009; Nat. Phys.; 5; 412; Shafir; et al; 2010; New J. Phys.; 12; 073032; Neufeld; et al; 2019; Nat. Commun.; 10; 405). In contrast, ellipticities of odd harmonics remain rather small independent of the pulse duration. In the further analysis of the results we discuss the impact of the relative intensities of the two pulses, their relative carrier-to-envelope phase and the pulse duration on the ellipticity of the harmonics.;

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