Experimental tests of QED in bound and isolated systems – Lesson 2
Lucile Julien · 2012
S 1 states are metastable On another hand, in helium the 2 3 P states are narrower (1.6 MHz) since they cannot easily decay to the ground state The spectroscopy of helium atom : fine structure 2 3 S 1 1083 nm 2 3 P 0 2 3 P 1 2 3 P 2 29.6 GHz 2.3 GHz A lot of experiments have been performed in 4 He to measure the fine structure intervals of the 2 3 P manifold Metastable 2 3 S atoms are populated by discharge either in a cell or in an atomic beam Other spectroscopic measurements in heliumPrecise frequency measurements of optical energy intervals provide a test of two-electron Lamb shift calculations• Absolute frequency measurements of the 2 3 S 1 -2 3 P 0,1,2 transitions at 1083 nm, with a frequency comb, give access to the 2 3 S -2 3 P and 2 3 P Lamb shifts (Florence)• Measurement of the two-photon 2 3 S 1 -3 3 D 1 transition at 762 nm (Paris) provides the ionization energy of the 2 3 S state and a precise determination of the 2 3 S Lamb shift through theoretical calculations on the 3 3 D 1 level