Bogdan Borca

Multiphoton detachment of a negative ion by an elliptically polarized, monochromatic laser field

The quasistationary quasienergy state approach (QQES) is applied to the analysis of partial (n-photon) decay rates and angular distributions (ADs) of photoelectrons produced by an elliptically polarized laser field. The problem is formulated for a weakly bound electron with an energy E0 in the threedimensional δ-model potential (which approximates the short-range potential of a negative ion) interacting with a strong monochromatic laser field having an electric vector F (ωt) .T he resu lts presented cover weak (perturbative), strong (nonperturbative), and superstrong field regimes as well as a wide interval of frequencies ω extending from the tunnelling (¯ hω �| E0|) and multiphoton (¯ ω |E0|). For a weak laser field, exact equations for the normalization factor and for the Fourier coefficients of the QQES wavefunction at the origin (|r |→ 0) (that are key elements of the QQES approach for a δ-model potential) as well as for the detachment amplitudes are analysed analytically using both standard Rayleigh– Schr¨ odinger perturbation theory (PT) in the intensity, I ,o f the lase rfi eld and Brillouin–Wigner PT expansions involving the exact (complex) quasienergy � . The lowest-order perturbative results for the n-photon ADs are presented in analytic form, and the parametrization of ADs in terms of polarization- and angular-independent atomic parameters is discussed for the general case of elliptical polarization. The major emphasis is on the analysis of an ellipticity induced distortion of three-dimensional ADs and, especially, on the elliptic dichroism (ED) effect, i.e. the dependence of the photoelectron yield in a fixed direction n on the sign of the ellipticity (or on the helicity) of a laser field. The dominant role of binding potential effects for a correct description of ED and threshold effects is demonstrated, and the intimate relationship between atomic ED factors and scattering phases o ft hedetached electron is established for multiphoton detachment, including the above-threshold case.

Stabilization of Bound State Decay in an Intense Monochromatic High-Frequency Field

The formalism of complex quasienergies is used for exact calculation of the field-dependent decay rate for a weakly bound particle (in the model of a three-dimensional zero-range potential) in a strong monochromatic laser field. It is shown that the adiabatic (quasistationary) stabilization regime in this model occurs at frequencies ω exceeding the binding energy and only in a limited intensity range. A simple estimate is obtained for the critical field of stabilization breakdown. The effect may be observed for the decay of H− ions in the field of a neodymium laser of femtosecond duration.

Static-electric-field behaviour in negative ion detachment by an intense, high-frequency laser field

Based upon the exact numerical solution of the complex quasienergy problem for a 3-dimensional short-range potential as well as upon analytical evaluations, we demonstrate for any finite frequency ω that the action of an ultra-intense laser field (with electric vector F(ωt)) on a weakly bound atomic system may be described by the cycle-averaging of results for an instantaneous static electric field of strength |F(ωt)|.

The effect of static applied magnetic and electric fields on the dielectronic recombination of

A new calculation was performed of the dielectronic recombination rate coefficient for the ion, in cases for which static magnetic and electric fields are applied simultaneously in the collision region. The intermediate-state Hamiltonian was diagonalized in a basis of states of fixed n (principal quantum number of the high Rydberg state electron) and included the paramagnetic, diamagnetic and Stark terms. Our results showed enhancements of , when both magnetic and electric fields were present, beyond what occurred for an applied electric field alone. Generally, these additional enhancements depended nontrivially upon the angle between the two applied fields. Also, in a region of elevated magnetic field strengths , the diamagnetic term was found to play an important role, when .