79 research outputs found
Dressed autoionising states and light-induced continuum structures in an intense laser field
No full textResults are presented for Floquet calculations of photodetachment rates from a one-dimensional model atom irradiated by intense laser light. Light-induced quasibound states are found to originate from the movement of poles of the multichannel scattering matrix on the Riemann energy surface. The appearance of new bound states of the negative Hydrogen ion, recently predicted, is related to the motion of resonance poles that correspond to autoionising states in the absence of the field. A number of pole trajectories, leading to light-induced states, are discussed for the one-dimensional model atom. The Floquet method allows one to represent the wave function of a quantum system in a laser field, as an infinite sum of harmonic basis functions. In any practical calculation this infinite sum must be truncated. The consequences of representing the wave function, via the Floquet method, by a finite sum of harmonics is addressed. An illustration of these consequences is made by way of a number of representative calculations performed on a one-dimensional model atom. Results are presented of calculations performed to determine the influence of a laser field, of low to moderate intensity, upon the partial and total photodetachment rates of the negative Hydrogen ion, H(^-). Using the R-matrix Floquet method, a study is undertaken into the detachment of an electron from the ion, via multiphoton transitions through one of several autodetaching resonances of the ion. The discussion focuses on the influence of the laser field upon auto detaching pathways. It is found that the laser may induce structure into the continuum that does not exist in the absence of the laser field, or, conversely, may suppress field-free structure. In the latter case, the suppression of structure is related to the appearance of laser-induced degeneracies
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Final Report: Interaction of Two Electron Atoms with Light. [November 1, 1994 - October 31, 1998]
No full textDuring the tenure of this grant we focused our efforts on the treatment of (1) the behavior of the negative hydrogen ion, H{sup {minus}}, in a strong laser field (whose intensity extends well into the nonperturbative regime), and (2) two-electron escape from a helium atom, He, by synchrotrons light. The calculations for H{sup {minus}} were done using perimetric coordinates {mu}, {nu}, and {omega}, which are linear combinations of the three interparticle distances, together with the three Euler angles. The algebra involved in the implementation of the perimetric coordinate system can be quite formidable. However, we formulated [1] a general and tractable decomposition of the two-electron wavefunction which greatly facilitated the algebra. A complex Sturmian-type basis set, in these coordinates, was employed. One of the main advantages of the perimetric coordinates is that the matrices representing the system's Hamiltonian and its interaction with the radiation field are sparse, so that storage requirements and the number of operations are minimized. The correlation between the electrons is fully incorporated. Indeed, perimetric coordinates are ideally suited to situations where the correlation is strong; each of the planes {mu} = 0, {nu} = 0, and {omega} = 0 has the special significance that the electrons lie on a line passing through the nucleus--on the same side, of the nucleus if {mu} or {nu} is zero, and on opposite sides if {omega} = 0. We found [2] that the two-electron probability distribution for H{sup {minus}}+ has maxima on each of these planes
Perturbation theory for multiphoton ionization without knowledge of the final-state wave function
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