The cross sections for double photoionization of helium and the ratios of double to single ionization have been measured from the double-ionization threshold to 820 eV. The results are in very good agreement with several recent calculations.
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Copyright American Physical Society, used with permission
Samson, J. A.,
Stolte, W. C.,
He, Z. X.,
Cutler, J. N.,
Bartlett, R. J.
Double photoionization of Helium.
Physical Review A, 57(3),