Suppression of Photoionization by a Static Field

The dc field Stark effect is studied theoretically for atoms in high intensity laser fields. We prove that the first-order perturbation corrections for the energy and photoionization rate vanish when the dc field strength serves as a perturbational strength parameter. Our calculations show that by applying a dc field in the same direction as the polarization direction of the ac field, the photoinduced ionization rate is almost entirely suppressed. This suppression is attributed to changes in the phase shift of the continuum atomic wave functions which can be controlled by the dc field.

Figure 1

The ratio ${\Gamma }_0/{\epsilon }_{\mathrm{ac}}^2$ plotted vs the dc field strength ${\epsilon }_{\mathrm{dc}}$. ${\Gamma }_0$ is the photoionization rate as obtained from our numerically exact Floquet calculations. The dotted line is for ${\epsilon }_{\mathrm{ac}}=0.005\mathrm{a}.\mathrm{u}.$, the dashed line for ${\epsilon }_{\mathrm{ac}}=0.035\mathrm{a}.\mathrm{u}.$, while the solid line is for ${\epsilon }_{\mathrm{ac}}=0.075\mathrm{a}.\mathrm{u}.$. Note that the ionization rate is totally suppressed regardless of the value of ${\epsilon }_{\mathrm{ac}}$. The dot-dashed line represents the results of the golden rule formula in (3).

Figure 2

The dependence of the PI decay rate of a model 3D xenon atom in a combination of a cw laser field and a static field on the dc field strength. An electron in the field-free atom in this model is assumed to be moving under the influence of an effective radial potential of the form $V(r)=-V_0/{cosh}^2(ar)$, where $V_0=1.074\mathrm{a}.\mathrm{u}.$ and $a=2.814\mathrm{a}.\mathrm{u}.$. The laser field strength is ${ϵ}_{\mathrm{ac}}=0.035\mathrm{a}.\mathrm{u}.$ while the laser frequency is ${\omega }_L=0.5\mathrm{a}.\mathrm{u}.$ throughout.

Figure 3

The dependence of the PI decay rate of hydrogen atom in a combination of a cw laser field and a static field on the dc field strength. The laser field strength is ${ϵ}_{\mathrm{ac}}=0.025\mathrm{a}.\mathrm{u}.$ and the laser frequency is ${\omega }_L=0.6330\mathrm{a}.\mathrm{u}.$ throughout. The ionization decay rate due to the dc field alone is added for comparison in the dashed line.