Figure 1

Comparison of HHG spectra in unaligned (dashed red) and aligned at $\Theta =0^{°}$ (solid black) samples of CO${}_2$: (a) with 800-nm drive field at $3.5\times {10}^{14}$ W cm${}^{-2}$ (from Ref. [4]); (b) with 1300-nm drive field at $1.0\times {10}^{14}$ W cm${}^{-2}$. The arrows mark the position of the minima.Reuse & Permissions

Figure 2

(a)–(d) HHG ratios between aligned and unaligned CO${}_2$ as a function of photon energy and aligning angle for driving intensities: (0.8, 1.0, 1.2, and 1.6) $\times {10}^{14}$ W cm${}^{-2}$ respectively. (e) Cut of figures (a)–(d) along $\Theta =0^{°}$. (f) Position of the interference minimum as a function of laser intensity.Reuse & Permissions

Figure 3

(a) Electron excursion time vs photon energy (short trajectories) calculated classically for CO${}_2$. Black and white solid lines correspond to the conditions of the present work and those of Ref. [9] respectively. Increasing thickness represents increasing intensity (0.8–$1.6)\times {10}^{14}$ W cm${}^{-2}$ (black) and (0.6–$2.0)\times {10}^{14}$ W cm${}^{-2}$ (white). The dashed line corresponds to the experiment of Ref. [4], at $3.5\times {10}^{14}$ W cm${}^{-2}$. The background shading represents the dynamical interference between $X$ and $B$ channels: constructive (light) or destructive (dark). The vertical lines in (a) and (b) show the position of the structural minimum. (b) Calculated harmonic amplitudes in CO${}_2$ with 1300-nm drive field and an intensity of $1.3\times {10}^{14}$ W cm${}^{-2}$ for the $X$ (circles) and $B$ (triangles) channels as well as the total amplitude (squares). (c) Calculated total harmonic yield at three intensities spanning the range used in this work.Reuse & Permissions