Free-free Gaunt factors of hydrogen-like ions in dense quantum plasmas

Abstract

The free-free Gaunt factors as functions of the initial electron energy εi of hydrogen-like ions are investigated, for a typical photon absorption energy of ω= 10 Ry in strongly coupled quantum plasmas, where the screened Coulomb interactions are modeled as the cosine-Debye–Hückel potentials. The free-free Gaunt factors in the strongly coupled quantum plasmas exhibit remarkably different features from the ones in the weakly coupled classical plasmas. The results of the free-free processes are featured with the resonances when the screening length κ is close to the critical screening length κnlc(the corresponding bound state |nl〉 merges into the continuum state when the screening length approaches the value). It is found that these resonances can be roughly classified into two types: the enhanced broad resonance and the shape-type narrow resonance. The former one appears when κ→κnsc, where a virtual state |ns〉 with near-zero-energy exists, while the latter one (κ→κnlc, l≥1) is formed by the temporary capture of a continuous electron by an effective short-range potential. Note that when the screening length is close to both κnpc and κn sc, the Gaunt factors would exhibit a superimposition of a narrow shape-type resonance and a broad resonance. Given that the free-free Gaunt factor is a summation over the angular momentum, the main contributions of different partial waves to the resonance behavior are further analyzed.