Ion-Energy Dependence of Asymmetric Dissociation of ${\mathbf{D}}_2$ by a Two-Color Laser Field

Two-color (800 and 400 nm) short (45 fs) linearly polarized pulses are used to ionize and dissociate ${\mathrm{D}}_2$ into a neutral deuterium atom and a deuteron. The yields and energies of the ions are measured left and right along the polarization vector. As the relative phase of the two colors is varied, strong yield asymmetries are found in the ion-energy regions traditionally identified as bond softening, above-threshold dissociation and rescattering. The asymmetries in these regions are quite different. A model based on the dynamic coupling by the laser field of the gerade and ungerade states in the molecular ion accounts for many of the observed features.

Figure 1

Schematic of dissociation processes for ${\mathrm{D}}_2$ (not to scale). Traditional BS and ATD processes are indicated by thin arrows. The additional process enabled by the second harmonic is indicated by the thicker double-ended arrow. Rescattering is indicated by a dashed arrow.

Figure 2

Density plot of the asymmetry of ${\mathrm{D}}^{+}$ ion emission from ${\mathrm{D}}_2$ as a function of ion energy and phase $\varphi$ between 800 and 400 nm radiation. The panel on the left shows a log plot of the total ion yield as a function of ion energy with decades indicated by tic marks.

Figure 3

Similar to Fig. 2: comparison of experiment (a) and theory (b) for the one and two-photon regions of ion energy (0–2 eV). The left hand panels show log plots of the measured (calculated) energy spectra integrated over all phases, while the bottom panels show the asymmetries integrated over one-photon (0–0.3 eV) and two-photon (0.3–2 eV) regions of the spectrum. Also shown in the bottom panels are plots measured and calculated for the rescattering region from Fig. 2 (4–6 eV).