Phase shift induced from the dc Stark effect in an atom interferometer comprised of four copropagating laser beams

We observed the phase shift of the atomic wave function induced from the dc Stark effect using an atom interferometer comprised of four copropagating traveling laser beams. We calculated the interference signal for the interferometer in the case of a thermal atomic beam. By comparing the observed interference fringes with the calculated ones, the difference between the polarizabilities of the P-3(1) state and the S-1(0) state of calcium was obtained to be alpha(P-3(1)) - alpha(S-1(0)) = (13.4+/-2.0) X 10(-24) cm(3). This value was consistent with that deduced from the Stark frequency shift.