We define and measure the ratio (R) of the vector ac-Stark effect (or light
shift) in the 6S_1/2 and 5D_3/2 states of a single trapped barium ion to 0.2%
accuracy at two different off-resonant wavelengths. We earlier found R =
-11.494(13) at 514.531nm and now report the value at 1111.68nm, R = +0.4176(8).
These observations together yield a value of the matrix element,
previously unknown in the literature. Also, comparison of our results with an
ab initio calculation of dynamic polarizability would yield a new test of
atomic theory and improve the understanding of atomic structure needed to
interpret a proposed atomic parity violation experiment.Comment: 12 pages, 11 figures, in submission to PR