PNC-Stark Interference

In the second class of experiments the PNC-induced 1 moment interferes with a Stark-induced 1 moment instead of an Ml moment. When an external static electric field , is applied to the atom, a Stark 1 amplitude 15 appears with a form similar to the PNC amplitude in Eq. (19)  

The Stark-PNC form of interference is utilized in experiments with heavy atoms at Berkeley and Paris, and in many experiments with hydrogen. Here we present a qualitative sketch of the scheme used at Paris and Berkeley. The basic idea, originally pointed out by Bouchiat and Bouchiat, is that an electronic polarization (i.e., a nonzero expectation value of the electronic angular momentum ])) in the excited state of the atom is induced by absorption of a circularly polarized photon directed perpendicular to an applied static electric field. 

For definiteness, let the static field be in the jc direction, = jX, and let the incident photon have its momentum k in the y direction, so that its circularly polarized electric vector is given [cf. (21)] by E, = o(z - it x)/V2. We look for electronic polarization in the z direction given by 

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