Control of Electron Localization in Deuterium Molecular Ions using an Attosecond Pulse Train and a Many-Cycle Infrared Pulse

We demonstrate an experimental control of electron localization in deuterium molecular ions created and dissociated by the combined action of an attosecond pulse train and a many-cycle infrared (IR) pulse. The attosecond pulse train is synthesized using both even and odd high order harmonics of the driving IR frequency so that it can strobe the IR field once per IR cycle. An asymmetric ejection of the deuterium ions oscillates with the full IR period when the APT-IR time-delay is scanned. The observed control is due to the creation of a coherent superposition of $1s{\sigma }_g$ and $2p{\sigma }_u$ states via interference between one-photon and two-photon dissociation channels.

Figure 1

The XUV characterization and schematic of the control of electron localization in ${\mathrm{D}}_2$. (a) Photoelectron energy spectrum of Ar produced by the Ar harmonics using the two-color (800 nm and 400 nm) driving field. (b) The XUV photon energies from 11th to 17th harmonics (blue arrows) are superimposed on ${\mathrm{D}}_2$ potential curves within the Fanck-Condon (FC) transition region. The red arrow denote the IR-assisted coupling between the $1s{\sigma }_g$ and $2p{\sigma }_u$ states (in the united-atom designation) of ${\mathrm{D}}_2^{+}$. Inset: A geometrical sketch of the setup showing the XUV-IR propagation along the $x$ axis, their polarization vectors and the time-of-flight (TOF) direction along the $z$ axis, and the gas jet along the $y$ axis.

Figure 2

Experimental signatures for the directional ejection of ${\mathrm{D}}^{+}$ ions. The ion TOF spectra when ${\mathrm{D}}_2$ is exposed to, (a) XUV only, and (c) XUV with IR. Left and Right denote forward and backward ${\mathrm{D}}^{+}$ ions, respectively. Insets: zoom around the ${\mathrm{D}}^{+}$ TOF. The momentum distribution of the ${\mathrm{D}}^{+}$ ions in the $xz$ plane for the cases, (b) XUV only, and (d) XUV with IR.

Figure 3

The asymmetry parameter $A$ versus the APT-IR time delay. Circles: experimental data, solid line: theory. The data have been smoothened using three-point running-average of raw data. The error bars denote the statistical error in total ${\mathrm{D}}^{+}$ counts for the averaged data. The positive delays correspond to the APT followed by the IR pulse.

Figure 4

The mechanism of the electron localization control. (a) The time evolution of $1s{\sigma }_g$ and $2p{\sigma }_u$ populations following the launch of a FC wave packet for zero delay (dashed line) in the IR pulse ($I\approx {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$, 40 fs). Insets: Zoom on population dynamics for the zero delay and for 0.67 fs delay (dashed curves). (b) Experimental and theoretical ${\mathrm{D}}^{+}$ ion energies integrated over all delays.