Recombination in strong laser fields: Manifestation of a slow drift

The dynamics of recombination in ultrastrong laser fields is studied by numerical simulations for one-dimensional model atomic systems. A nonmonotonic behavior of the ground-state final population as a function of the laser field amplitude is demonstrated. It is attributed to both the slow drift of the electron wave packet and the nontrivial field dependence of the lifetime of the eigenstates of the Kramers-Henneberger well.

Figure 1

The population of the ground state of the model long-range atomic potential in the recombination process as a function of the field intensity ${\epsilon }_0$ in the case of the field being switched off at $t_f$ equal exactly to $3T$, solid line; at the time instant $t_f$ of a maximum population in the vicinity of $3T$ (see comment in the text), dashed line; at the time instant $t_f$ of a maximum population in the vicinity of $2T$, short-dashed line; the packet’s initial position $x_0=-2{\epsilon }_0∕{\omega }^2$, upper plot; the results averaged over the initial positions in the interval $-2{\epsilon }_0∕{\omega }^2\pm 1\mathrm{a.u.}$, lower plot.

Figure 2

As in Fig. 1, upper plot, but for the ground state of a square well potential.

Figure 3

The population of the ground state of the square well potential in the recombination process (upper plot) and ionization process (lower plot) as functions of the field intensity ${\epsilon }_0$ in the case of the field being switched off at $t_f$ equal exactly to $10T$, $20T$, and $30T$.

Figure 4

Ground-state population of a square potential well after exactly three optical periods as a function of the field intensity for various frequencies.

Figure 5

The time evolution of the wave packet recombination in the square well potential for different values of the field intensity. The level of blackening is proportional to the squared modules of the wave function.

Figure 6

As in Fig. 5 but for a model long-range atomic potential.

Figure 7

The time evolution of the ground-state population in the case of a square well potential for the field intensity ${\epsilon }_0=5\mathrm{a.u.}$