Two-photon ionization of helium for 23S and 21S states

Two-photon ionization of He atom from its excited metastable
2^{3}S
and
2^{1}S
states is studied within the framework of the perturbation theory. Cross sections and ratios for circularly and linearly polarized laser light are obtained in the wavelength ranges 3180-3950 Å and 3650-5100 Å for
2^{3}S
and
2^{1}S
states, respectively. The effects of the quasi-resonant intermediate states and the states omitted in the truncated summation method are analyzed.