Original research articleTopological charge determination of linearly polarized Lorentz-Gaussian vortex beam

Focusing properties of linearly polarized Lorentz-Gaussian vortex beams was investigated by vector diffraction theory, from which topological charge determination method is proposed. Results show that the focal pattern can be altered considerably by topological charge, and for certain condition, the number of dark spots along one coordinate direction equals to topological charge, and the number of intensity lines crossing focal pattern along the other coordinate direction minus topological charge is one. The intensity lines across focal pattern get weaker for higher topological charge, which leads to the boundaries among dark spots become blurring. Focal shift value of the most out dark peak increases on increasing topological charge, and the dependence curve is monotonous. Topological charge can be obtained according to dependence curve even for fractional topological charge.