Measurement of the Absolute Photoionization Cross Section for the 5P3/2 State of 87Rb in a Vapor Cell Magneto-optic Trap

We report the measurement of the absolute photoionization cross section for the 5P(3/2) state of Rb-87 at wavelength of 473 nm, which results in the photoelectron energies of 33 meV above the ionization threshold, using cold atoms confined in a vapor- loaded magneto- optical trap. The Rb-87 5P(3/2) photoionization cross section at 473nm is determined to be sigma(PI) = 10.5 +/- 2.2 Mb. Considering the spatial distribution of the trapped atoms, the average intensity (I-PI) over bar of the ionization laser seen by an atom in the MOT instead of ionizing laser intensity I-PI is used in our calculations for the photoionization cross sections. The excited state fraction is also accurately estimated using the latest experimental result.