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We study quantum mechanically the influence of an external laser field on the antihydrogen (H-) formation cross sections in ground and excited states (2s,2p) via the three-body recombination process inside a dense plasma of antiprotons and positrons, supposed to be the most efficient mechanism for cold and trapped antihydrogen. The plasma screening is considered in the framework of a Debye- Hückel potential. The laser polarization is chosen to be parallel to the incident momentum of the passive positron. The modifications due to the presence of the laser field are found to be quite significant both quantitatively and qualitatively for all the states. In the presence of a laser, the H formation cross sections are found to be suppressed significantly with respect to the field-free situation particularly in the ground state, while the excited slate cross sections are in general enhanced at very low incident energies but are again suppressed at higher energies except for some special cases. The sensitivity of the formation cross sections with respect to the Debye length are also studied both in the laser-assisted and in the field-free situations. At very low incident energies, the ground state multiphoton formation is found to enhance with the increase in Debye screening, while the reverse is true for the excited states. These findings should have important implications for future H- studies. [ABSTRACT FROM AUTHOR]

The free-free transition is studied for an electron-hydrogen atom in ground state when a low-energy electron (external) is injected into hydrogenic plasma in the presence of an external homogenous, monochromatic, and linearly polarized laser field. The effect of plasma screening is considered in the Debye-HUckel approximation. The calculations are performed in the soft photon limit. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the electron exchange. The laser-assisted differential and total cross sections are calculated for single-photon absorption or emission and no-photon exchange in the soft photon limit, the laser intensity being much less than the atomic field intensity. The calculations have been earned out for various values of Debye parameter, ranging from 0.005 to 0.12. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situation. A significant difference is noted for the singlet and triplet cross sections. The suppression is much more in the triplet states. [ABSTRACT FROM AUTHOR]

The free-free transition is studied for an electron-hydrogen atom system in the ground state at very low incident energies in the presence of an external homogeneous, monochromatic, and linearly polarized laser field. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron-exchange interactions, short-range interactions, as well as of long-range interactions. The laser-assisted differential as well as total elastic cross sections are calculated for single-photon absorption or emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situations. A significant difference is noted in the singlet and the triplet cross sections, [ABSTRACT FROM AUTHOR]

The modification in the dynamics of the electron-impact ionization process of a Li+ ion due to an intense linearly polarized monochromatic laser field (nye.2e) is studied theoretically using coplanar geometry. Significant laser modifications are noted due to multiphoton effects both in the shape and magnitude of the triple-differential cross sections (TDCSs) with respect to the field-free (FF) situation. The net effect of the laser field is to suppress the FF cross sections in the zeroth-order approximation [Coulomb-Volkov (CV)] of the ejected electron wave function, while in the first order [modified Coulomb-Volkov (MCV)], the TDCSs are found to be enhanced or suppressed depending on the kinematics of the process. The strong FF recoil dominance for the (e,2e) process of an ionic target at low incident energy is destroyed in the presence of the laser field. The FF binary-to-recoil ratio changes remarkably in the presence of the laser field, particularly at low incident energies. The difference between the multiphoton CV and the FF results indicates that for the ionic target, the Kroll-Watson sum rule does not hold well at the present energy range in contrast to the neutral atom (He) case. The TDCSs are found to be quite sensitive with respect to the initial phase of the laser field, particularly at higher incident energies. A significant qualitative difference is noted in the multiphoton ejected energy distribution (double-differential cross sections) between the CV and the MCV models. Variation of the TDCSs with respect to the laser phase is also studied. [ABSTRACT FROM AUTHOR]