Measurement of the branching ratios for 6P 1/2 decays to 6S 1/2 and 5D 3/2 in 138 Ba + are reported with the decay probability from 6P 1/2 to 5D 3/2 measured to be p = 0.268177 ± (37)stat − (20)sys. This result differs from a recent report by 12σ. A detailed account of systematics is given and the likely source of the discrepancy is identified. The new value of the branching ratio is combined with a previous experimental results to give a new estimate of τ = 7.855(10) ns for the 6P 1/2 lifetime. In addition, ratios of matrix elements calculated from theory are combined with experimental results to provide improved theoretical estimates of the 6P 3/2 lifetime and the associated matrix elements. arXiv:1905.06523v1 [physics.atom-ph]

The uniformity of the intensity and phase of laser beams is crucial to high-performance atom interferometers. Inhomogeneities in the laser intensity profile cause contrast reductions and systematic effects in interferometers operated with atom sources at micro-Kelvin temperatures, and detrimental diffraction phase shifts in interferometers using large momentum transfer beam splitters. We report on the implementation of a socalled top-hat laser beam in a long-interrogation-time cold-atom interferometer to overcome the issue of the inhomogeneous laser intensity encountered when using Gaussian laser beams. We characterize the intensity and relative phase profiles of the top-hat beam and demonstrate its gain in atom-optics efficiency over a Gaussian beam, in agreement with numerical simulations. We discuss the application of top-hat beams to improve the performance of different architectures of atom interferometers.