Absolute cross sections for the photoionization of the 6s6p ^{1}P excited state of barium

Absolute photoionization cross sections for the 6s6p ${}_{}{}^1{}_{}{}^{}$P excited state of Ba have been measured in the threshold region and found to agree substantially with theory, thus resolving previous discrepancies. Use was made of the ‘‘magic’’ angle applied to the relative orientation of the linear polarizations of the exciting and ionizing lasers; at this orientation angle the measured cross section is the same as if the excited state were populated isotropically. This phenomenon, which has general application to electric dipole photoabsorption processes, allowed us to make the measurements in two different ways, with excellent agreement between them.