R-matrix Floquet theory of multiphoton processes: IX. Three-photon laser-induced degenerate states in argon

Abstract

A bound state and an autoionizing state of a complex atom, resonantly coupled by a multiphoton process in a strong laser field, can become degenerate at a certain laser frequency and intensity. These states are referred to as laser-induced degenerate states or LIDS. The ab initio, fully nonperturbative R-matrix Floquet method has been used to study the behaviour of LIDS coupled by three photons in argon. A simple single-photon model has been successfully applied to interpret the calculation and to predict a further degeneracy at a higher frequency and intensity.

Static and dynamic polarizability for C2+ in Rydberg states

“…Close to zero field intensity, the trajectory of one state remains adiabatically close to the real axis, while the other trajectory corresponding to quasi-energy of the second state has an imaginary part which remains constant for all photon frequencies. 16,17 The zero-field position of the autoionizing state changes with ω, being scaled at the complex energy field-free width of the autoionizing state and E a is the energy of the autoionizing state. The tuning frequency is ω tune = E a − E b , with E b the field free position of the 'bound' Rydberg state.…”

Theoretical calculation of atomic data for plasma spectroscopy

“…There have been several theoretical methods introduced to describe multiphoton processes in atoms (Knight et al, 1990;Cyr et al, 1997;Kylstra & Joichain, 1998;Fearnside, 1998;Paspalakis et al, 2000). Of these calculations, only those employing the R-matrix Floquet (RME) method couple the field to the ion non-perturbatively, and only those of Latinne et al (1995) and Cyr et al (1997), explicitly investigated the laserinduced modification of doubly excited states, that is to say, the interplay of LIDS. Specifically, the frequency and the intensity of the light field can be adjusted such that the energy and the width of the dressed ground state coincide with the energy and width of a dressed autoionizing state.…”

Intensity dependence of resonances profiles in multiphoton partial detachment rates of

“…For the present calculations the R-matrix Floquet approach has been employed as implemented by Purvis et al 1993, modified by van der Hart andCyr (1997) and used by van der Hart and Fearnside (1997). The technical intricacies of the method having been covered extensively in earlier articles in this series (Burke et al 1990, 1991, Dörr et al 1992, only the most important aspects of the R-matrix Floquet technique are touched upon and the interested reader is referred to the above-mentioned articles for further details.…”

“…In the latter case a rather complicated model predicted LIDS associated with the 1s 2 1 S e and 2s 2 1 S e states of the ion. Recently, Cyr et al (1997) considered a three-photon coupling between the ground and an autoionizing state of argon and found further degeneracies. They also developed a simple but effective model to describe these LIDS based on a one-photon coupling of a virtual ground state to an autonionizing state.…”

“…For each such frequency region, the partial two-photon detachment rates (of the relevant symmetry) shall be presented for a wide range of laser intensities, a range sufficient to illustrate a very strong intensity dependence in the resonance profile associated with excitation of the resonant doubly excited state in question. Section 4 offers an interpretation of these results in terms of the LIDS discussed by Latinne et al (1995) and Cyr et al (1997).…”