ElecSus: A program to calculate the electric susceptibility of an atomic   ensemble
  We present a computer program and underlying model to calculate the electric susceptibility of a gas, which is essential to predict its absorptive and dispersive properties. Our program focusses on alkali-metal vapours where we use a matrix representation of the atomic Hamiltonian in the completely uncoupled basis in order to calculate transition frequencies and strengths. The program calculates various spectra for a weak-probe laser beam in an atomic medium with an applied axial magnetic field. This allows many optical devices to be designed, such as Faraday rotators/filters, optical isolators and circular polarisation filters. Fitting routines are also provided with the program which allows the user to perform optical metrology by fitting to experimental data. 
Mark A. Zentile, James Keaveney, Lee Weller, Daniel J. Whiting,   Charles S. Adams and Ifan G. Hughes
physics.atom-ph physics.optics quant-ph