Steering the Nuclear Motion in Singly Ionized Argon Dimers with Mutually Detuned Laser Pulses

We demonstrate that the vibrational nuclear motion of singly ionized argon dimers can be controlled with two ultrashort laser pulses of different wavelengths. In particular, we observe a striking “gap” in the pump-probe-delay-dependent kinetic-energy release spectrum only if the probe-pulse wavelength exceeds the pump-pulse wavelength. This “frustrated dissociation effect” is reproduced by our two-state quantum mechanical model, validating its interpretation as a pump-pulse-initiated population transfer between dipole-coupled Born-Oppenheimer electronic states of the dissociating $\mathrm{Ar}_2{}^{+}$ molecular ion. Our numerical results also reproduce the measured collapse and fractional revival of the oscillating $\mathrm{Ar}_2{}^{+}$ nuclear wave packet, and, for single-pulse dissociation, the decrease of the kinetic-energy release with increasing laser wavelength.

Figure 1

Sketch of the $\mathrm{Ar}_2{}^{+}$ dissociation dynamics in two mutually delayed and detuned ultrashort laser pulses with central frequencies ${\omega }_s$ and ${\omega }_l$ that allow resonant one-photon transitions at internuclear distances $R$ indicated by $C$, $D$ and $B$, $E$, respectively. The red profile shows the nuclear probability density of the ${\mathrm{Ar}}_2$ ground state.

Figure 2

(a) Measured KER spectra for ${\mathrm{Ar}}_2(1,0)$ in a single 60 fs laser pulse at various wavelengths. (b) Measured and calculated wavelength-dependent KER at the maximal yields in (a).

Figure 3

(a) Measured ${\mathrm{Ar}}_2(1,0)$ KER spectrum as a function of the pump-probe time delay for 60 fs laser pulses with a peak intensity of ${10}^{14}\mathrm{W}/{\mathrm{cm}}^2$. (b) Corresponding calculated KER spectrum. The green dashed vertical line indicates zero time delay. The orange and yellow curves labeled with $0.8–1.0\mathrm{eV}$ and $0.35–0.4\mathrm{eV}$ are partial fragment yields obtained by integrating the spectra in (a) and (b) over the KER ranges from 0.8 to 1.0 eV and 0.35 to 0.4 eV, respectively.

Figure 4

(a) Measured time-dependent KER spectrum as in Fig. 3a, but for an increased pump-pulse peak intensity of $9\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ and an extended delay range. (b) Dissociation yield obtained by integration over the KER range in (a). (c) The calculated dissociation yield for the same KER range.