Measurement of the ratio of double-to-single photoionization of helium at 2.8 keV using synchrotron radiation

Abstract

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He"*""""/He"*" = 1.6%±0.3% at /zv==2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Aberg, who predict 1.7%.

Fundamental Aspects of Atomic Photoionization with High-Brightness Light Sources

“…[81,82] The ratio was found to be 1.5 ± 0.2%, and essentially constant over this entire range. This indicates that a constant ratio has been reached.…”

Mechanisms of Photo Double Ionization of Helium by 530 eV Photons

“…This process has been termed shake-off. In the high photon energy limit, the ratio of the total double to total single ionization cross sections converges to a constant R = 1.67 %, a limit expected for the shake-off [4,5]. At low photon energies it has been argued by Samson [3] that one electron absorbs the photon and knocks out the second electron in an (e,2e) like collision.…”

Photo double ionization of He by circular and linear polarized single-photon absorption

“…This question has been heavily studied over the past few years 4 . The first experimental and theoretical studies on two-electron ejection by photoabsorption considered only the total cross section for double ionization and the ratio of cross sections for double to single ionization [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Today, these questions are settled over the full energy range from threshold to 10 keV.…”