Laser pulse propagation in ionizing air: A semianalytical approach

We use an approximate method to describe the propagation of a short laser p ulse in air. It is shown that the plasma generation via multiphoton ionizat ion acts as an effective higher order nonlinear term. This analogy provides a simple physical interpretation on how the competing effects between focu sing and defocusing can lead to a long range propagation. Our results, at l east qualitatively, are in agreement with experimental observations and wit h previous numerical studies.