Bi-chromatic driver enabled control of high harmonic generation in atomic targets

Abstract

We investigated the high-order harmonic generation from interacting time-delayed, linearly polarized bi-chromatic laser pulses with the atomic target. The frequency ratio of secondary to primary fields ($\omega_2/\omega_1$), along with the carrier-envelope-phase (CEP) and respective time-delay between the two pulses, are very instrumental in controlling the ionization of the electron and so the quantum dynamics in the continuum. We observed an optimum CEP (φ) and time delay ($t_\mathrm{d}$) for a given bi-chromatic frequency ratio, giving maximum cutoff energy. We studied the effect of CEP and time delay for a fixed frequency ratio and observed that the harmonic cutoff could be controlled in an experimentally feasible way. Moreover, the harmonic yield in the energy range 140 eV–240 eV was also calculated, and it was observed that the harmonic yield scales as $\propto -\phi^{5/6}$. The attosecond pulses for different CEP were also calculated by superposing the harmonics in the same energy range, and ${\sim}200$ pulses were observed with peak intensity decreasing with CEP, following the variation of respective harmonic yield with CEP