Attosecond Photoelectron Spectroscopy of Electron Tunneling in a Dissociating Hydrogen Molecular Ion

We demonstrate the potential of intense-field pump, attosecond probe photoelectron spectroscopy to monitor electron tunneling between the two protons during dissociative ionization of the hydrogen molecule, with attosecond temporal and Angstrom-scale spatial resolution.

Figure 1

Attosecond probing of electron dynamics in ${\mathrm{H}}_2^{+}$. (a) A vibrational wave packet in the ground state ${}^2\Sigma _g^{+}$ is created by strong-field ionization of ${\mathrm{H}}_2$. As it moves towards larger $R$, the recollision of the liberated electron with the parent ${\mathrm{H}}_2^{+}$ excites it into the dissociative state ${}^2\Sigma _u^{+}$ (RCE). A time-delayed XUV probe monitors the dynamics in ${\mathrm{H}}_2^{+}$ by one-photon ionization (creating ${\mathrm{H}}_2^{2+}$). (b) The pump-probe pair: an intense few-cycle IR pulse and an attosecond XUV pulse. The IR pulse has a carrier of $\lambda =800\mathrm{nm}$ and is 5 fsec long; the XUV pulse is centered at $\lambda =15\mathrm{nm}$ and is 350 asec long.

Figure 2

Photoelectron spectra on the left detector as a function of the XUV probe delay time $t_X$. XUV duration is 350 asec; the wavelength ${\lambda }_{\mathrm{XUV}}=15\mathrm{nm}$. The vertical scale, shown as a color bar, is in arbitrary units.

Figure 3

(a) shows the contribution of the first ${\mathrm{H}}_2$ ionization event to the asymmetry in the photoelectron spectra between the left and the right detector. (b) shows the total asymmetry in the photoelectron spectra between the left and the right detector, including all ionization events weighted by their respective probabilities. Positive asymmetry corresponds to higher signal at the left detector. The XUV probe pulse is 350 asec; the wavelength ${\lambda }_{\mathrm{XUV}}=15\mathrm{nm}$.