Probing tunneling dynamics of dissociative ${\mathrm{H}}_2$ molecules using two-color bicircularly polarized fields

Probing and manipulating the electronic motion in the ultrafast laser molecular interaction provides the pathways for quantum imaging and controlling chemical reactions. Recently, the emerging application of attosecond metrology of ultrafast electron dynamics has accessed the time scale of the most fundamental processes in molecular chemical reactions. Here, we probe the tunneling dynamics of internuclear-dependent dissociative reaction of ${\mathrm{H}}_2$ with angular streaking using two-color bicircularly polarized femtosecond laser pulses. By measuring high-resolution photoelectron spectroscopy, we disentangle the orientation and internuclear-distance dependent effect of the long-range Coulomb potential and the initial phase on molecular-frame photoelectron momentum distributions, and stereo extract the phase gradient of the tunneling electron wave packets and Wigner time delay during the dissociative ionization using two-color bicircular fields. The work has an insight into the clocking of ultrafast spatiotemporal photoelectron dynamics and the quantum control of molecular chemical processes via sculptured circular fields, which can be applied to polyatomic molecules.

Figure 1

The attoclock scheme using bicircular fields for the dissociative reaction of ${\mathrm{H}}_2$ molecules. (a) The combined potential created by the Coulomb field of the ${\mathrm{H}}_2$ molecule and the laser field. The bound electron escapes the potential through tunneling. (b) The experimental geometry. The fragmentation of ${\mathrm{H}}_2$ molecules by two-color corotating bicircular fields is measured by the COLTRIMS spectrometer.

Figure 2

Measured joint photoelectron-nuclear energy spectrum and two-dimensional photoelectron momentum distributions. (a) The joint photoelectron-nuclear energy spectrum of above-threshold multiphoton dissociative ionization. The nuclear energy spectrum integrated over the electron energy spectrum is shown in the left panel. (b)–(d) Measured photoelectron angular distributions correlated to the 1ω channel (b), net-2ω channel (c), and net-3ω channel (d).

Figure 3

(a) The measured correlated electron emission angle with the ${\mathrm{H}}^{+}$ ion emission angle. (b) The simulated result using the TDSE for the net-2ω channel. (c), (d) The simulated correlated electron emission angle with ${\mathrm{H}}^{+}$ ion emission angle for the net-2ω and net-3ω channels using the MO-QTMC model.

Figure 4

(a), (b) The most probable electron emission angle ${\theta }_{\mathrm{ele}}$ extracted from the experiment, TDSE and MO-QTMC model for the net-2ω (a) and the net-3ω (b) channels, respectively. (c), (d) The most probable electron emission angle simulated using the MO-QTMC model for the net-2ω (c) and net-3ω (d) channels with and without the long-range Coulomb potential, respectively. The black solid and dashed curves depict the results of MO-QTMC with and without the Coulomb interaction after tunneling, respectively. The red curves indicate the deflect angle because of the initial phase.

Figure 5

(a), (b) The initial phase ${\varphi }_{\mathrm{ini}}$ with respect to the initial transverse momentum $p_i$ for the net-2ω (a) and net-3ω (b) channels. (c), (d) The initial phase gradient ${\varphi }_{\mathrm{ini}}^{\prime }$ and the Wigner time delay $\mathrm{\Delta }{\tau }_{\mathrm{w}}$ in the molecular frame for the net-2ω (c) and net-3ω (d) channels.