Formation of Ground-State Vibrational Wave Packets in Intense Ultrashort Laser Pulses

The formation of coherent vibrational wave packets in the electronic ground state of neutral molecules in intense ultrashort laser pulses and their subsequent detection by means of recently developed pump-probe experiments are discussed. The wave packet formation is due to the pronounced dependence of the strong-field ionization rate on the internuclear distance. This leads to a deformation of the initial wave function due to an internuclear-distance dependent depletion. The phenomenon is demonstrated with a time-dependent wave packet study for molecular hydrogen.

Figure 1

Time evolution of the ${\mathrm{H}}_2$ ground-state wave function in a laser pulse of 8 fs duration (peak intensity, $I=6\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$; wavelength, 800 nm; $t=0$, onset of pulse).

Figure 2

Expectation value of $⟨R⟩$ as a function of time during and after 800 nm laser pulses of 8 fs (dashed line) and 12 fs (solid line) duration and a peak intensity $I=6.0\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ ($t=0$, onset of pulse). Also shown is the result for a 12 fs pulse but reduced peak intensity $I=5.264\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ (chain).

Figure 3

Ionization yield predicted for the probe pulse of a pump-probe experiment with two identical pulses (800 nm, peak intensity $I=6.0\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$) of either 8 (solid line, left scale) or 12 fs (dashed line, right scale) duration is shown as a function of the delay time between the two pulse maxima.