Tensor polarizability of the 2 P11 state of He4 by electric-field level crossing

A measurement of the tensor polarizability of the 2 P11 state of atomic helium has been made by the electric-field level-crossing technique using an atomic-beam apparatus. The experimental procedure is as follows: An atomic beam containing metastable 2 S01 and 2 S13 helium atoms is produced by electron bombardment of ground-state helium atoms. The beam then passes through a region in which the atoms are subjected to a uniform, variable electric field. In this region the 2 S01 atoms are excited to the 2 P11 state by linearly polarized 20 582- (2 S01-2 P11) resonance radiation. The extreme uv photons emitted in the direction of the incident resonance light when the 2 P11 state decays to the ground state are counted. The sum intensity of the 584- (2 P11-1 S01) photons and the 601- (2 S01-1 S01) photons, due to the electric-field quenching of the 2 S01 atoms, is measured as a function of the applied electric field for the incident light polarized at 45°and 90°to the direction of the static electric field. From these measurements the tensor polarizability α2(2 P11) of the 2 P11 state is found to be (3.32 ± 0.10) × 10-23 cm3, in good agreement with the theoretically calculated value of 3.34 × 10-23 cm3. © 1974 The American Physical Society.