No abstract

Details of the dynamics of ultrastrong-field photoionization are studied for a one-dimensional model atom with a short-range potential. The wave packet's drift due to its scattering on the binding potential is analyzed. The Kramers-Henneberger frame transformation is generalized in such a way that the drift is formally included and the packet's shape becomes stable in the new frame. Such an approach in combination with the Ehrenfest description of the drift trajectory allows one to model the behavior of the packet and to interpret the details of the atomic stabilization.PACS number͑s͒: 42.50.Hz, 32.80.Rm, 32.80.Gc ‫ץ‬ 2 ‫ץ‬y 2 ͑ y,t ͒ϩU"yϩ␤͑ t ͒…͑ y,t ͒ϪF͑t ͒"yϩ␤͑ t ͒…͑ y,t ͒, ͑3͒wherePHYSICAL REVIEW A, VOLUME 61, 043402

Electron hopping transport along the DNA chain is studied theoretically by a straightforward numerical solution of the time-dependent Schrödinger equation. Results are given for the hole transition rates between two guanine bases bridged by sequences of the adenine-thymine bases with various lengths. Two models are considered: (i) with time-independent chain structure and (ii) with positions of bases on the bridge oscillating with time. It is shown that only the latter model is consistent with experimental data. The problem of the incoherence in the hopping transport mechanism is discussed.

Charge transfer in a donor -short bridge -acceptor system is studied within a simple model of a DNA molecule. A difference in transfer rates via two bridges containing similar bases though with opposite sequences is demonstrated. The result calls for experimental verification.

An adiabatic stabilization against photoionization consists in the fact that an electron wave packet ͑or at least its part͒ in an ultrastrong laser field moves as a whole in the rhythm of the field in the neighborhood of the nucleus instead of throwing away its small parts every time it passes the nucleus ͓1͔. This phenomenon can also be described as the packet's trapping in the time-averaged potential seen by the electron ͑Kramers-Henneberger well͒. A necessary condition for the model stabilization in one dimension is that the laser pulse is such that the solution of the classical Newton equation, also in the absence of the binding potential, has the mean velocity ͑i.e., the velocity averaged over the oscillation period͒ equal to zero. This is true, for example, for trapezoid field envelopes or for a cosine electric field with a rectangular envelope, but not for a sine pulse with the latter envelope.It has been known for a long time that the effect of the stabilization is weaker for two-or three-dimensional systems ͓2͔. This has been confirmed by Vazquez de Aldana et al. ͓3,4͔, who have numerically investigated the photoionization of a two-dimensional atom and have demonstrated that the stabilization is essentially hindered. A reason for that is that, apart from the strong electric force in the direction of the pulse polarization, there exists a magnetic force that causes a drift of the packet away from the nucleus ͓3,4͔. Below we show classically and demonstrate by ab initio numerical computations that it is in general impossible to choose such a field ramp-up that the magnetic drift could be avoided and that the latter effect can be compensated by an additional properly chosen constant magnetic field. In our opinion this is an interesting theoretical observation concerning the dynamics of the process, even though the magnitude of this magnetic field is now far beyond the experimentally accessible range.The atomic model we adopt is a shallow ͑i.e., such that the ionization energy of the bound state is small͒ rectangular potential well, for which the effect of tearing up of the packet into smaller pieces is small for the field intensities considered in this paper. Our observations would be valid also for long-range potentials ͓5͔, for which the packet also remains a connected structure during the evolution, and are in contrast with our former results for a deep potential well ͓6͔, for which numerous pieces of the packet exhibited some special dynamical effects.Consider a laser pulse with the electric-field amplitude equal to E x (y,t)ϭE 0 f (), ϭtϪky, during the switch-on stage 0рр 1 and E x (y,t)ϭE 0 cos(ϩ) for Ͼ 1 . We assume that 1 ϭ2n, n being an integer number. We are not concerned with the switch-off stage because it has no influence on the stabilization. The magnetic field is B z ϭ(Ϫ1/c)E x ϩB c , where we have admitted a constant magnetic component in addition to the magnetic field of the laser. The Newton equations of motion in two spatial dimensions areIf we make the dipole approximation now and retain...