Spatiotemporal Imaging of Ultrafast Molecular Motion: Collapse and Revival of the $\mathrm{D}_2{}^{+}$ Nuclear Wave Packet

We report on a real-time imaging of the ultrafast $\mathrm{D}_2{}^{+}$ rovibrational nuclear wave-packet motion performed using a combination of a pump-probe setup with 7 fs laser pulses and a “reaction-microscope” spectrometer. We observe fast dephasing (collapse) of the vibrational wave packet and its subsequent revival and prove rotational excitation in ultrashort laser pulses. Channel-selective Fourier analysis of the wave packet’s long-term ($\sim 3000\mathrm{fs}$) evolution allows us to resolve its individual constituents, revealing unique information on the mechanisms of strong-field ionization and dissociation.

Figure 1

(a) A scheme of the pump-probe experiment and the relevant potential curves of ${\mathrm{D}}_2$ and $\mathrm{D}_2{}^{+}$. The curves are shown for a field-free situation. The three-photon transition around $R\approx 1.9\AA$ is indicated by three arrows. (b) Schematic of the experimental geometry. $\theta$ denotes the measured ${\mathrm{D}}^{+}$ emission angle (and, thus, the orientation of the internuclear axis) relative to the laser polarization direction $\overrightarrow{\mathcal{E}}$.

Figure 2

(a) ${\mathrm{D}}^{+}$ kinetic energy spectrum as a function of the delay between the pump and the probe pulses. Numbers in the figure indicate the pathways discussed in the text. (b) The distribution of the $\mathrm{D}_2{}^{+}$ wave-packet probability density as a function of the internuclear distances $R$ and the delay between the pump and the probe pulses reconstructed from the experimental data. (c) Calculated density plot of $\mathrm{D}_2{}^{+}$ wave-packet propagation.

Figure 3

Measured CE yield of the ${\mathrm{D}}^{+}$ ions in the 3–4 eV energy interval as a function of the delay $\tau$ between the pump and the probe pulses. (a) Integrated over all emission angles $\theta$ relative to the laser polarization direction. (b) $0°\le \theta \le 10°$. (c) $20°\le \theta \le 30°$. (d) $40°\le \theta \le 50°$.

Figure 4

Fourier transform of the time-dependent CE yield in the (a) 3–3.5, (b) 3.5–4, (c) 4–4.5, and (d) 4.5–5 eV energy intervals and (e) of the dissociation yield. Thin vertical lines show the frequencies of the vibrational transitions known from the spectroscopic data [25]. Numbers on top of the figure indicate the corresponding transitions: The frequency $f({\nu }_{i,i+1})$ is denoted by the number $i$. Inset: Fourier transform of the time-dependent dissociation yield for low frequencies. Clear peaks due to the rotational transitions can be observed.