V. D. Mur

Multiple Colliding Electromagnetic Pulses: A Way to Lower the Threshold of e+e- Pair Production from Vacuum

The scheme of a simultaneous multiple pulse focusing on one spot naturally arises from the structural features of projected new laser systems, such as the Extreme Light Infrastructure (ELI) and High Power laser Energy Research (HiPER). It is shown that the multiple pulse configuration is beneficial for observing e+ e- pair production from a vacuum under the action of sufficiently strong electromagnetic fields. The field of focused pulses is described using a realistic three-dimensional model based on an exact solution of the Maxwell equations. The e+ e- pair production threshold in terms of electromagnetic field energy can be substantially lowered if, instead of one or even two colliding pulses, multiple pulses are focused on one spot. The multiple pulse interaction geometry gives rise to subwavelength field features in the focal region. These features result in the production of extremely short e+ e- bunches.

Strong field ionization rate for arbitrary laser frequencies.

A simple, analytical, nonrelativistic ionization rate formula for atoms and positive ions in intense ultraviolet and x-ray electromagnetic fields is derived. The rate is valid at arbitrary values of the Keldysh parameter and confirmed by results from ab initio numerical solutions of the single active electron, time-dependent Schrödinger equation. The proposed rate is particularly relevant for experiments employing the new free electron laser sources.

On e(+)e(-) pair production by colliding electromagnetic pulses

Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a realistic three-dimensional model of the electromagnetic field of the focused wave, which is an exact solution of the Maxwell equations. It has been shown that e+e− pair production can be experimentally observed when the intensity of each beam is I∼1026 W/cm2, which is two orders of magnitude lower than that for a single pulse.

Contribution to the theory of Lorentzian ionization

The probability wL of Lorentzian ionization, which arises when an atom or ion moves in a constant magnetic field, is calculated in the quasiclassical approximation. The nonrelativistic (v≲e2/ℏ=1, v is the velocity of the atom) and ultrarelativistic (v→c=137) cases are examined and the stabilization factor S, which takes account of the effect of the magnetic field on tunneling of an electron, is found.

The imaginary-time method for relativistic problems

A relativistic version of the imaginary-time method is presented. The method is used to calculate the probability w of ionization of a bound state by electric and magnetic fields of various configurations (including the case when the binding energy Eb is comparable to mc2). The formulas cover as limiting cases both the ionization of nonrelativistic bound systems (atoms and ions) and the case Eb=2mc2, when w equals the probability of electron-positron pair production from the vacuum in the presence of a strong field.

On the relativistic theory of tunneling

A relativistic generalization of the semiclassical theory of tunneling and multiphoton ionization of atoms and ions in the field of a high-intensity electromagnetic wave with linear, circular, and elliptic polarization is constructed. The exponential factor in the ionization probability is calculated for arbitrary values of adiabaticity parameter γ. In the case of low-frequency laser radiation, an asymptotically exact formula is derived for the ionization rate of the s atomic level, including the Coulomb, spin, and adiabatic corrections and the preexponential factor.

On the Zel’dovich regularization method in the theory of quasistationary states

Complex quasienergy and level width are calculated for a weakly bound atomic state in an intense circularly polarized monochromatic laser field using the method suggested by Zel’dovich for the regularization of divergent integrals with the Gamow wave function. It is demonstrated that this method converges, and the conditions for its applicability are indicated. These results are used to discuss the accuracy of the semiclassical approximation in the problems of ionization theory.

Coulomb problem for graphene with the gapped electron spectrum

The characteristics of charge carriers in graphene with dopants having charge Z and deposited onto a SiC substrate are analyzed. The closed set of explicit equations determining the spectrum of charge carriers are obtained for the case of the Coulomb potential modified at small distances. The critical values Zcr of the dopant charge at which the energy level with the given quantum numbers crosses the valence band boundary are determined. At Z < Zcr, for the lowest values of the orbital angular momentum, the position of the energy level corresponding to the bound state is obtained as a function of charge Z. For Z > Zcr, the position and width of the quasistationary state are calculated. The problem concerning the screening of the impurity charge is also considered.

Ionization of atoms and ions by intense laser radiation

The ionization of negative ions by ultrashort electromagnetic pulses, the multiphoton ionization of atoms beyond the perturbation theory taking into account the Coulomb interaction, and the relativistic theory of tunneling in application to the ionization problems have been analyzed. The main results have been obtained using the imaginary time method.

On the inclusion of the Coulomb interaction in the theory of multiphoton ionization

The Coulomb correction to the rate of multiphoton ionization of atoms and ions by intense laser radiation is derived for large Keldysh adiabaticity parameters using the imaginary time method. This correction increases the ionization rate by several orders of magnitude.