Interfacing light and single atoms with a lens
  We characterize the interaction between a single atom or similar microscopic system and a light field via the scattering ratio. For that, we first derive the electrical field in a strongly focused Gaussian light beam, and then consider the atomic response. Following the simple scattering model, the fraction of scattered optical power for a weak coherent probe field leads to unphysical scattering ratios above 1 in the strong focusing regime. A refined model considering interference between exciting and scattered field into finite-sized detectors or optical fibers is presented, and compared to experimental extinction measurements for various focusing strengths. 
Meng Khoon Tey, Gleb Maslennikov, Timothy C.H. Liew, Syed Abdullah   Aljunid, Florian Huber, Brenda Chng, Zilong Chen, Valer...