Radiative Decay of Doubly Excited States in Helium below theHe+(N=2)Ionization

Abstract

The radiative decay of (1)P(o) doubly excited states in helium has been investigated using a novel apparatus in which metastable atoms and vacuum ultraviolet photons are detected. The intensity ratio of the energetically narrow (sp,2n-)(1)P(o) and (2p,nd)(1)P(o) series to the broader (sp,2n+)(1)P(o) series is strikingly enhanced in comparison with conventional photoabsorption, photoion, or photoelectron measurements using synchrotron radiation. The experimental approach is a new way forward for the study of energetically narrow doubly excited states.

Intermanifold similarities in partial photoionization cross sections of helium

“…Yet, as has been demonstrated recently, interesting additional features such as radiative and relativistic effects emerge by, e.g., measuring the photon emission following the photo excitation [9,10,11,12]. It turns out that this signal reveals the splitting of the He + threshold due to spin-orbit coupling.…”

“…Therefore, this kind of disentanglement works well, as long as the effect of the perturber on the width of the resonances is small as it is the case for the cross sections σ N =5,N ′ and σ N =6,N ′ . The perturber 8, 6 8 , however, causes a drastic narrowing of the width of the state 7, 5 10 . This perturbation of the pattern cannot be compensated by expressing the energy in terms of the effective quantum defect.…”

Double Photoexcitation of Helium in a Strong dc Electric Field

“…Much more recently, it has become apparent that some of the photodoubly excited states also decay via fluorescence [3][4][5], and the superhigh resolution available at thirdgeneration light sources has enriched our understanding of these competing decay routes [6 -8]. An important aspect of the recent measurements is that as the N 2 threshold is approached states of triplet character can be directly excited from the ground state [8,9].…”

Two-photon resonant excitation of a doubly excited state in He atoms by high-harmonic pulses

“…Here, we focus on the helium atom as a nonlinear optical medium, since it is the simplest three-body system consisting of an atomic nucleus and two electrons, which can be rigorously treated in the theoretical description. One of the interesting properties of helium atoms is the presence of doubly excited states [16][17][18][19][20][21][22][23][24]13] All the doubly excited states of helium atoms are located far above the ionization threshold, and hence they autoionize. Although the doubly excited states of helium were first observed more than forty years ago using SOR [17], they are still under extensive investigation because helium is a proto-type system with electron-electron correlations.…”