Figure 1

(Color online) HGS obtained from a one-dimensional (1D) model Hamiltonian of Xe atom irradiated by a 50-oscillation sine-square pulse of bichromatic laser field composed of a strong laser field of frequency $\omega$ $(\lambda =800\mathrm{nm})$ and amplitude ${\epsilon }_1^{\text{in}}$ $(I_1^{\text{in}}\simeq 4.3\times {10}^{13}\mathrm{W}∕{\mathrm{cm}}^2)$ and a weak field of frequency $q\omega$ and amplitude ${\epsilon }_q^{\text{in}}$ $(I_q^{\text{in}}\simeq 3.5\times {10}^8\mathrm{W}∕{\mathrm{cm}}^2)$ for different values of $q$: $q=25$ [solid red (dark gray) line], 37 [dotted green (bright gray) line], and 52 [solid blue (dark gray) line]. HGS in the absence of the XUV field is shown in the dotted black (bright gray) line where the position of the cutoff is at the 15th harmonic. The harmonics above the 29th harmonic are enhanced in the addition of the XUV field, despite its small intensity. In addition, with respect to its center $q$, the distribution of the new harmonics in the HGS is symmetric [i.e., for $q=37$, $\sigma \left(33\omega \right)\simeq \sigma \left(41\omega \right)$, etc.] and upon variation of $q$ it shifts but remains almost invariant.Reuse & Permissions

Figure 2

(Color online) Top view [pink (dark gray) color—high intensity, yellow (bright gray) color—low intensity] of the absolute square of the Gabor-transformed acceleration expectation value [$(1∕50T){\int }_0^{50T}a\left(t\right)e^{-{(t-t_0)}^2∕{\tau }^2}{e}^{-i\Omega t}$, $\tau =0.1T$] of the quantum-mechanical simulation described in Fig. 1 for $q=52$, as a function of $t_0$ and $\Omega$.Reuse & Permissions